Methods of increasing muscle mass by administration of activin type 2 receptor antibodies

ABSTRACT

This disclosure provides ActRII-binding proteins such as anti-ActRIIA and anti-ActRIIB antibodies, and compositions and methods for making the ActRII-binding proteins. In certain aspects the ActRII-binding proteins inhibit, or antagonize ActRII activity. In addition, the disclosure provides compositions and methods for diagnosing and treating diseases and conditions associated muscle wasting; a fibrotic condition; an inflammatory, cardiovascular, pulmonary, musculoskeletal, neurologic, ocular, skeletal, autoimmune, or metabolic disease or condition; wound healing; and cancer, and other ActRII-mediated diseases and conditions.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. application Ser. No.15/456,392, filed Mar. 10, 2017, which claims the benefit of U.S.Provisional Appl. No. 62/306,354, filed Mar. 10, 2016, each of which isincorporated herein by reference.

REFERENCE TO SEQUENCE LISTING SUBMITTED ELECTRONICALLY

The content of the electronically submitted sequence listing in ASCIItext file APH-00402 SL.txt (Size: 182,831 bytes; and Date of Creation:Aug. 16, 2019) filed with the application is herein incorporated byreference in its entirety.

BACKGROUND

The transforming growth factor-beta (TGF-beta) family contains a varietyof growth factors that are known to exert biological effects on a largevariety of cell types in both vertebrates and invertebrates. Members ofthe TGF-beta family perform important functions during embryonicdevelopment in pattern formation and tissue specification and caninfluence a variety of differentiation processes, includingadipogenesis, myogenesis, chondrogenesis, cardiogenesis, hematopoiesis,neurogenesis, and epithelial cell differentiation. The family includesproteins that are variously described as Growth and DifferentiationFactors (GDFs), Bone Morphogenetic Proteins (BMPs), activins andinhibins.

TGF-beta family members transduce signals through a mechanism thatincludes a multistep process in which the TGF-beta family member binds atype II serine/threonine kinase receptor expressed on the cell surface,the type II receptor forms a heteromeric complex with a cognate type Ireceptor and activates the type I receptor through phosphorylation, theactivated type-I receptor phosphorylates and activates Smad proteinsthat transduce the signal from the cytoplasm to the nucleus, and nuclearSmad oligomers bind to DNA and associate with transcription factors toregulate the expression of target genes.

Two related type II TGF-beta receptor family members, ActRIIB andActRIIA, have been identified as type II receptors for activin A andactivin B and other TGF-beta family members including BMP7, BMP9, BMP10,GDF1, GDF3, GDF8 (myostatin), GDF11, and Nodal (Yamashita et al., J.Cell Biol. 130:217-226 (1995); Lee et al., PNAS 98:9306-9311 (2001); Yeoet al., Mol. Cell 7:949-957 (2001); and Oh et al., Genes Dev. 16:2749-54(2002)). ALK4 and ALK7 are the primary type I TGF-beta receptor familymember receptors for activin A and activin B, respectively.

Alterations in the expression and activity of members of the TGF-betaligand and receptor families have been proposed to be associated with avariety of disorder and conditions including muscle, bone, neurologicaland metabolic disorders and conditions, and cancer. It is an object ofthis disclosure to provide ActRII antagonists and uses for the same inthe diagnosis and treatment, prevention and/or amelioration of a diseaseor condition associated with ActRII and/or ActRII ligands.

BRIEF SUMMARY

The disclosure provides activin receptor type II (ActRII)-bindingproteins and methods of using the ActRII-binding proteins. In particularaspects, the ActRII-binding proteins are capable of inhibiting orblocking the binding of ActRII to one or more cognate ActRII ligandsand/or one or more cognate ActRI receptors. In some aspects, theActRII-binding proteins are capable of inhibiting or blocking thebinding to ActRII to an ActRII ligand (e.g., activin A, activin B, GDF1,GDF3, GDF8 (myostatin), GDF11, BMP6, BMP7, BMP9, or BMP10). Thedisclosure also provides methods of using ActRII-binding proteins forthe diagnosis, or treatment, prevention and/or amelioration of a diseaseor condition associated with ActRII expression and/or elevatedActRII-mediated signaling. Such diseases or conditions include, but arenot limited to, muscle disorders such as degenerative muscle disease,muscular dystrophy, muscle atrophy, or muscle wasting disorders; afibrotic condition; an inflammatory, autoimmune, cardiovascular,pulmonary, musculoskeletal, skeletal, ocular, neurologic, or metabolicdisease or condition; obesity; wound healing; and cancer.

In some aspects, the ActRII-binding protein specifically binds ActRIIB.In further aspects, the provided ActRII-binding protein specificallybinds ActRIIB and has at least one characteristic selected from thegroup consisting of: (a) competes with an ActRII ligand (e.g., activinA, activin B, GDF1, GDF3, GDF8 (myostatin), GDF11, BMP6, BMP7, BMP9, orBMP10) for binding to ActRIIB; (b) decreases the phosphorylation of ALK4and/or ALK7 in cells expressing ActRIIB and ALK4 and/or ALK7 in thepresence of an ActRIIB ligand (e.g., activin A and/or GDF8 (myostatin));(c) decreases the phosphorylation of Smads (e.g., Smad2 and/or Smad3) incells expressing ActRIIB in the presence of an ActRIIB ligand (e.g.,activin A and/or GDF8); and (d) binds to ActRIIB with a K_(D) of ≤1 nMand ≥1 pM (e.g., as determined by BIACORE® analysis). In some aspects,the ActRIIB-binding protein has 2, 3, or 4 of the above characteristics.In some aspects, the ActRIIB-binding protein has at least 2 or at least3 of the above characteristics. In further aspects, the ActRIIB-bindingprotein competes for binding to ActRIIB with an antibody having anActRIIB-binding VH and VL pair disclosed herein. In further aspects, theActRIIB-binding protein is an anti-ActRIIB antibody or anActRIIB-binding antibody fragment.

In some aspects, the ActRII-binding protein specifically binds ActRIIBand ActRIIA. In further aspects, the provided ActRII-binding proteinspecifically binds ActRIIB and ActRIIA and has at least onecharacteristic selected from the group consisting of: (a) competes withan ActRII ligand (e.g., activin A, activin B, GDF1, GDF3, GDF8(myostatin), GDF11, BMP6, BMP7, BMP9, or BMP10) for binding to ActRIIBand/or ActRIIA; (b) decreases the phosphorylation of ALK4 and/or ALK7 incells expressing ActRIIB and/or ActRIIA, and ALK4 and/or ALK7, in thepresence of an ActRIIB and/or ActRIIA ligand (e.g., activin A and/orGDF8 (myostatin)); (c) decreases the phosphorylation of Smads (e.g.,Smad2 and/or Smad3) in cells expressing ActRIIB and/or ActRIIA in thepresence of an ActRIIB and/or ActRIIA ligand (e.g., activin A and/orGDF8); and (d) binds to ActRIIB with a K_(D) of ≤1 nM and ≥1 pM (e.g.,as determined by BIACORE® analysis). In some aspects, the ActRIIB- andActRIIA-binding protein has 2, 3, or 4 of the above characteristics. Insome aspects, the ActRIIB- and ActRIIA-binding protein has at least 2 orat least 3 of the above characteristics. In further aspects, theActRIIB-binding protein competes for binding to ActRIIB and ActRIIA withan antibody having an ActRIIB- and ActRIIA binding VH and VL pairdisclosed herein. In further aspects, the ActRIIB- and ActRIIA-bindingprotein is an anti-ActRIIB and ActRIIB antibody or an ActRIIB- andActRIIB binding antibody fragment.

In some aspects, the ActRII-binding protein specifically binds ActRIIA.In further aspects, the provided ActRII-binding protein specificallybinds ActRIIA and has at least one characteristic selected from thegroup consisting of: (a) competes with an ActRII ligand (e.g., activinA, activin B, GDF1, GDF3, GDF8 (myostatin), GDF11, BMP6, BMP7, BMP9, orBMP10) for binding to ActRIIA; (b) decreases the phosphorylation of ALK4and/or ALK7 in cells expressing ActRIIA and ALK4 and/or ALK7 in thepresence of an ActRIIA ligand (e.g., activin A and/or GDF8 (myostatin));(c) decreases the phosphorylation of Smads (e.g., Smad2 and/or Smad3) incells expressing ActRIIA in the presence of an ActRIIA ligand (e.g.,activin A and/or GDF8); and (d) binds to ActRIIA with a K_(D) of ≤1 nMand ≥1 pM (e.g., as determined by BIACORE® analysis). In some aspects,the ActRIIA-binding protein has 2, 3, or 4 of the above characteristics.In some aspects, the ActRIIA-binding protein has at least 2 or at least3 of the above characteristics. In further aspects, the ActRIIA-bindingprotein competes for binding to ActRIIA with an antibody having anActRIIA-binding VH and VL pair disclosed herein. In further aspects, theActRIIA-binding protein is an anti-ActRIIA antibody or anActRIIA-binding antibody fragment.

In some aspects, the ActRII-binding protein comprises a set ofcomplementary determining regions (CDRs): heavy chain variable region(VH)-CDR1, VH-CDR2, VH-CDR3, light chain variable region (VL)-CDR1,VL-CDR2 and VL-CDR3, wherein the CDRs are present in a heavy chainvariable region (VH) and a light chain variable region (VL) pairdisclosed in Table 1. In some aspects, the ActRII-binding proteincomprises a set of CDRs present in a VH and a VL pair selected from thegroup consisting of: (a) a VH sequence of SEQ ID NO:2, 16, 22, 28, 34,or 40, and a VL sequence of SEQ ID NO:9, and wherein the protein bindsActRIIB, (b) a VH sequence of SEQ ID NO:63 or 77, and a VL having theamino acid sequence of SEQ ID NO:70, and wherein the protein bindsActRIIB; (c) a VH sequence of SEQ ID NO:45 or 57, and a VL sequence ofSEQ ID NO:50, and wherein the protein binds ActRIIB; (d) a VH sequenceof SEQ ID NO:84, 98, 105, 112, or 119, and a VL sequence of SEQ IDNO:91, and wherein the protein binds and ActRIIB and activin receptortype IIA (ActRIIA), and (e) a VH sequence of SEQ ID NO:125, and a VLsequence of SEQ ID NO:132, and wherein the protein binds ActRIIA.

In some aspects, the ActRII-binding protein comprises a set of CDRspresent in a VH having the amino acid sequence of SEQ ID NO:144 and a VLhaving the amino acid sequence of SEQ ID NO:151, and wherein the proteinbinds ActRIIB.

In some aspects, the ActRII-binding protein comprises a set of CDRspresent in a VH having the amino acid sequence of SEQ ID NO:165 and a VLhaving the amino acid sequence of SEQ ID NO:172, and wherein the proteinbinds ActRIIA and ActRIIB.

In additional aspects, the ActRII-binding protein specifically bindsActRII and comprises a set of CDRs: VH-CDR1, VH-CDR2, VH-CDR3, VL-CDR1,VL-CDR2, and VL-CDR3, wherein the set of CDRs is identical to, or has atotal of one, two, three, four, five, six, seven, eight, nine, ten, orfewer than ten, amino acid substitutions, deletions, and/or insertionsfrom a reference set of CDRs in which: (a)(i) VH-CDR1 has the amino acidsequence of SEQ ID NO:3, 17, 23, 29, 35 or 41; (ii) VH-CDR2 has theamino acid sequence of SEQ ID NO:4, 18, 24, 30, 178, or 36; (iii)VH-CDR3 has the amino acid sequence of SEQ ID NO:5; (iv) VL-CDR1 has theamino acid sequence of SEQ ID NO:10; (v) VL-CDR2 has the amino acidsequence of SEQ ID NO:11; and (vi) VL-CDR3 has the amino acid sequenceof SEQ ID NO:12; and wherein the protein binds ActRIIB; (b)(i) VH-CDR1has the amino acid sequence of SEQ ID NO:64 or 78; (ii) VH-CDR2 has theamino acid sequence of SEQ ID NO:65 or 79; (iii) VH-CDR3 has the aminoacid sequence of SEQ ID NO:66 or 80; (iv) VL-CDR1 has the amino acidsequence of SEQ ID NO:71; (v) VL-CDR2 has the amino acid sequence of SEQID NO:72; and (vi) VL-CDR3 has the amino acid sequence of SEQ ID NO:73;and wherein the protein binds ActRIIB; (c)(i) VH-CDR1 has the amino acidsequence of SEQ ID NO:3 or 58; (ii) VH-CDR2 has the amino acid sequenceof SEQ ID NO:4 or 59; (iii) VH-CDR3 has the amino acid sequence of SEQID NO:46; (iv) VL-CDR1 has the amino acid sequence of SEQ ID NO:51; (v)VL-CDR2 has the amino acid sequence of SEQ ID NO:52; and (vi) VL-CDR3has the amino acid sequence of SEQ ID NO:53; and wherein the proteinbinds ActRIIB; (d)(i) VH-CDR1 has the amino acid sequence of SEQ IDNO:85, 99, 106, 166, or 113; (ii) VH-CDR2 has the amino acid sequence ofSEQ ID NO:86, 100, 107, 114, 167, or 120; (iii) VH-CDR3 has the aminoacid sequence of SEQ ID NO:87, 101, 108, 115, 168, or 121; (iv) VL-CDR1has the amino acid sequence of SEQ ID NO:92, or 173; (v) VL-CDR2 has theamino acid sequence of SEQ ID NO:93, 153, or 174; and (vi) VL-CDR3 hasthe amino acid sequence of SEQ ID NO:94, or 175; and wherein the proteinbinds ActRIIB and ActRIIA; or (e)(i) VH-CDR1 has the amino acid sequenceof SEQ ID NO:126; (ii) VH-CDR2 has the amino acid sequence of SEQ IDNO:127; (iii) VH-CDR3 has the amino acid sequence of SEQ ID NO:128; (iv)VL-CDR1 has the amino acid sequence of SEQ ID NO:133; (v) VL-CDR2 hasthe amino acid sequence of SEQ ID NO:134; and (vi) VL-CDR3 has the aminoacid sequence of SEQ ID NO:135; and wherein the protein binds ActRIIA.

In additional aspects, the ActRII-binding protein specifically bindsActRIIB and comprises a set of CDRs: VH-CDR1, VH-CDR2, VH-CDR3, VL-CDR1,VL-CDR2, and VL-CDR3, wherein the set of CDRs is identical to, or has atotal of one, two, three, four, five, six, seven, eight, nine, ten, orfewer than ten, amino acid substitutions, deletions, and/or insertionsfrom a reference set of CDRs in which (i) VH-CDR1 has the amino acidsequence of SEQ ID NO:145; (ii) VH-CDR2 has the amino acid sequence ofSEQ ID NO:146; (iii) VH-CDR3 has the amino acid sequence of SEQ IDNO:147; (iv) VL-CDR1 has the amino acid sequence of SEQ ID NO:152; (v)VL-CDR2 has the amino acid sequence of SEQ ID NO:153; and (vi) VL-CDR3has the amino acid sequence of SEQ ID NO:154.

In additional aspects, the ActRII-binding protein specifically binds ActIIRA and ActRIIB and comprises a set of CDRs: VH-CDR1, VH-CDR2, VH-CDR3,VL-CDR1, VL-CDR2, and VL-CDR3, wherein the set of CDRs is identical to,or has a total of one, two, three, four, five, six, seven, eight, nine,ten, or fewer than ten, amino acid substitutions, deletions, and/orinsertions from a reference set of CDRs in which (i) VH-CDR1 has theamino acid sequence of SEQ ID NO:166; (ii) VH-CDR2 has the amino acidsequence of SEQ ID NO:167; (iii) VH-CDR3 has the amino acid sequence ofSEQ ID NO:168; (iv) VL-CDR1 has the amino acid sequence of SEQ IDNO:173; (v) VL-CDR2 has the amino acid sequence of SEQ ID NO:174; and(vi) VL-CDR3 has the amino acid sequence of SEQ ID NO:175.

In some aspects, the ActRII-binding protein specifically binds ActRIIand comprises a set of CDRs in which: (a)(i) VH-CDR1 has the amino acidsequence of SEQ ID NO:3, 17, 23, 29, 35 or 41; (ii) VH-CDR2 has theamino acid sequence of SEQ ID NO:4, 18, 24, 30, 178, or 36; (iii)VH-CDR3 has the amino acid sequence of SEQ ID NO:5; (iv) VL-CDR1 has theamino acid sequence of SEQ ID NO:10; (v) VL-CDR2 has the amino acidsequence of SEQ ID NO:11; and (vi) VL-CDR3 has the amino acid sequenceof SEQ ID NO:12; and wherein the protein binds ActRIIB; (b)(i) VH-CDR1has the amino acid sequence of SEQ ID NO:64 or 78; (ii) VH-CDR2 has theamino acid sequence of SEQ ID NO:65 or 79; (iii) VH-CDR3 has the aminoacid sequence of SEQ ID NO:66 or 80; (iv) VL-CDR1 has the amino acidsequence of SEQ ID NO:71; (v) VL-CDR2 has the amino acid sequence of SEQID NO:72; and (vi) VL-CDR3 has the amino acid sequence of SEQ ID NO:73;and wherein the protein binds ActRIIB; (c)(i) VH-CDR1 has the amino acidsequence of SEQ ID NO:3 or 58; (ii) VH-CDR2 has the amino acid sequenceof SEQ ID NO:4 or 59; (iii) VH-CDR3 has the amino acid sequence of SEQID NO:46; (iv) VL-CDR1 has the amino acid sequence of SEQ ID NO:51; (v)VL-CDR2 has the amino acid sequence of SEQ ID NO:52; and (vi) VL-CDR3has the amino acid sequence of SEQ ID NO:53; and wherein the proteinbinds ActRIIB; (d)(i) VH-CDR1 has the amino acid sequence of SEQ IDNO:85, 99, 106, 166, or 113; (ii) VH-CDR2 has the amino acid sequence ofSEQ ID NO:86, 100, 107, 114, 167, or 120; (iii) VH-CDR3 has the aminoacid sequence of SEQ ID NO:87, 101, 108, 115, 168, or 121; (iv) VL-CDR1has the amino acid sequence of SEQ ID NO:92, or 173; (v) VL-CDR2 has theamino acid sequence of SEQ ID NO:93, 153, or 174; and (vi) VL-CDR3 hasthe amino acid sequence of SEQ ID NO:94, or 175; and wherein the proteinbinds ActRIIB and ActRIIA; or (e)(i) VH-CDR1 has the amino acid sequenceof SEQ ID NO:126; (ii) VH-CDR2 has the amino acid sequence of SEQ IDNO:127; (iii) VH-CDR3 has the amino acid sequence of SEQ ID NO:128; (iv)VL-CDR1 has the amino acid sequence of SEQ ID NO:133; (v) VL-CDR2 hasthe amino acid sequence of SEQ ID NO:134; and (vi) VL-CDR3 has the aminoacid sequence of SEQ ID NO:135; and wherein the protein binds ActRIIA.

In some aspects, the ActRII-binding protein specifically binds ActRIIBand comprises a set of CDRs in which (i) VH-CDR1 has the amino acidsequence of SEQ ID NO:145; (ii) VH-CDR2 has the amino acid sequence ofSEQ ID NO:146; (iii) VH-CDR3 has the amino acid sequence of SEQ IDNO:147; (iv) VL-CDR1 has the amino acid sequence of SEQ ID NO:152; (v)VL-CDR2 has the amino acid sequence of SEQ ID NO:153; and (vi) VL-CDR3has the amino acid sequence of SEQ ID NO:154.

In some aspects, the ActRII-binding protein specifically binds ActIIRAand ActRIIB and comprises a set of CDRs in which (i) VH-CDR1 has theamino acid sequence of SEQ ID NO:166; (ii) VH-CDR2 has the amino acidsequence of SEQ ID NO:167; (iii) VH-CDR3 has the amino acid sequence ofSEQ ID NO:168; (iv) VL-CDR1 has the amino acid sequence of SEQ IDNO:173; (v) VL-CDR2 has the amino acid sequence of SEQ ID NO:174; and(vi) VL-CDR3 has the amino acid sequence of SEQ ID NO:175.

In some aspects, the ActRII-binding protein specifically binds ActRIIand comprises a set of CDRs that has a total of one, two, three, four,five, six, seven, eight, nine, ten, fewer than ten, or zero, amino acidsubstitutions, deletions, and/or insertions from a reference set of CDRsin which: (a)(i) VH-CDR1 has the amino acid sequence of SEQ ID NO:3;(ii) VH-CDR2 has the amino acid sequence of SEQ ID NO:4; (iii) VH-CDR3has the amino acid sequence of SEQ ID NO:5; (iv) VL-CDR1 has the aminoacid sequence of SEQ ID NO:10; (v) VL-CDR2 has the amino acid sequenceof SEQ ID NO:11; and (vi) VL-CDR3 has the amino acid sequence of SEQ IDNO:12; and wherein the protein binds ActRIIB; (b)(i) VH-CDR1 has theamino acid sequence of SEQ ID NO:17; (ii) VH-CDR2 has the amino acidsequence of SEQ ID NO:18; (iii) VH-CDR3 has the amino acid sequence ofSEQ ID NO:5; (iv) VL-CDR1 has the amino acid sequence of SEQ ID NO:10;(v) VL-CDR2 has the amino acid sequence of SEQ ID NO:11; and (vi)VL-CDR3 has the amino acid sequence of SEQ ID NO:12; and wherein theprotein binds ActRIIB; (c)(i) VH-CDR1 has the amino acid sequence of SEQID NO:23; (ii) VH-CDR2 has the amino acid sequence of SEQ ID NO:24;(iii) VH-CDR3 has the amino acid sequence of SEQ ID NO:5; (iv) VL-CDR1has the amino acid sequence of SEQ ID NO:10; (v) VL-CDR2 has the aminoacid sequence of SEQ ID NO:11; and (vi) VL-CDR3 has the amino acidsequence of SEQ ID NO:12; and wherein the protein binds ActRIIB; (d)(i)VH-CDR1 has the amino acid sequence of SEQ ID NO:29; (ii) VH-CDR2 hasthe amino acid sequence of SEQ ID NO:30; (iii) VH-CDR3 has the aminoacid sequence of SEQ ID NO:5; (iv) VL-CDR1 has the amino acid sequenceof SEQ ID NO:10; (v) VL-CDR2 has the amino acid sequence of SEQ IDNO:11; and (vi) VL-CDR3 has the amino acid sequence of SEQ ID NO:12; andwherein the protein binds ActRIIB; (e)(i) VH-CDR1 has the amino acidsequence of SEQ ID NO:35; (ii) VH-CDR2 has the amino acid sequence ofSEQ ID NO:36; (iii) VH-CDR3 has the amino acid sequence of SEQ ID NO:5;(iv) VL-CDR1 has the amino acid sequence of SEQ ID NO:10; (v) VL-CDR2has the amino acid sequence of SEQ ID NO:11; and (vi) VL-CDR3 has theamino acid sequence of SEQ ID NO:12; and wherein the protein bindsActRIIB; (f)(i) VH-CDR1 has the amino acid sequence of SEQ ID NO:41;(ii) VH-CDR2 has the amino acid sequence of SEQ ID NO: 178; (iii)VH-CDR3 has the amino acid sequence of SEQ ID NO:5; (iv) VL-CDR1 has theamino acid sequence of SEQ ID NO:10; (v) VL-CDR2 has the amino acidsequence of SEQ ID NO:11; and (vi) VL-CDR3 has the amino acid sequenceof SEQ ID NO:12; and wherein the protein binds ActRIIB; (g)(i) VH-CDR1has the amino acid sequence of SEQ ID NO:64; (ii) VH-CDR2 has the aminoacid sequence of SEQ ID NO:65; (iii) VH-CDR3 has the amino acid sequenceof SEQ ID NO:66 or 80; (iv) VL-CDR1 has the amino acid sequence of SEQID NO:71; (v) VL-CDR2 has the amino acid sequence of SEQ ID NO:72; and(vi) VL-CDR3 has the amino acid sequence of SEQ ID NO:73; and whereinthe protein binds ActRIIB; and (h)(i) VH-CDR1 has the amino acidsequence of SEQ ID NO:78; (ii) VH-CDR2 has the amino acid sequence ofSEQ ID NO:79; (iii) VH-CDR3 has the amino acid sequence of SEQ ID NO:80;(iv) VL-CDR1 has the amino acid sequence of SEQ ID NO:71; (v) VL-CDR2has the amino acid sequence of SEQ ID NO:72; and (vi) VL-CDR3 has theamino acid sequence of SEQ ID NO:73; and wherein the protein bindsActRIIB; (i)(i) VH-CDR1 has the amino acid sequence of SEQ ID NO:3; (ii)VH-CDR2 has the amino acid sequence of SEQ ID NO:4; (iii) VH-CDR3 hasthe amino acid sequence of SEQ ID NO:46; (iv) VL-CDR1 has the amino acidsequence of SEQ ID NO:51; (v) VL-CDR2 has the amino acid sequence of SEQID NO:52; and (vi) VL-CDR3 has the amino acid sequence of SEQ ID NO:53;and wherein the protein binds ActRIIB; (j)(i) VH-CDR1 has the amino acidsequence of SEQ ID NO:58; (ii) VH-CDR2 has the amino acid sequence ofSEQ ID NO:59; (iii) VH-CDR3 has the amino acid sequence of SEQ ID NO:46;(iv) VL-CDR1 has the amino acid sequence of SEQ ID NO:51; (v) VL-CDR2has the amino acid sequence of SEQ ID NO:52; and (vi) VL-CDR3 has theamino acid sequence of SEQ ID NO:53; and wherein the protein bindsActRIIB; (k)(i) VH-CDR1 has the amino acid sequence of SEQ ID NO:85;(ii) VH-CDR2 has the amino acid sequence of SEQ ID NO:86; (iii) VH-CDR3has the amino acid sequence of SEQ ID NO:87; (iv) VL-CDR1 has the aminoacid sequence of SEQ ID NO:92; (v) VL-CDR2 has the amino acid sequenceof SEQ ID NO:93; and (vi) VL-CDR3 has the amino acid sequence of SEQ IDNO:94; and wherein the protein binds ActRIIB and ActRIIA; (l)(i) VH-CDR1has the amino acid sequence of SEQ ID NO:99; (ii) VH-CDR2 has the aminoacid sequence of SEQ ID NO:100; (iii) VH-CDR3 has the amino acidsequence of SEQ ID NO:101; (iv) VL-CDR1 has the amino acid sequence ofSEQ ID NO:92; (v) VL-CDR2 has the amino acid sequence of SEQ ID NO: 153;and (vi) VL-CDR3 has the amino acid sequence of SEQ ID NO:94; andwherein the protein binds ActRIIB and ActRIIA; (m)(i) VH-CDR1 has theamino acid sequence of SEQ ID NO:106; (ii) VH-CDR2 has the amino acidsequence of SEQ ID NO:107, (iii) VH-CDR3 has the amino acid sequence ofSEQ ID NO 108; (iv) VL-CDR1 has the amino acid sequence of SEQ ID NO:92;(v) VL-CDR2 has the amino acid sequence of SEQ ID NO: 153; and (vi)VL-CDR3 has the amino acid sequence of SEQ ID NO:94; and wherein theprotein binds ActRIIB and ActRIIA; (n)(i) VH-CDR1 has the amino acidsequence of SEQ ID NO:113; (ii) VH-CDR2 has the amino acid sequence ofSEQ ID NO:114; (iii) VH-CDR3 has the amino acid sequence of SEQ IDNO:115; (iv) VL-CDR1 has the amino acid sequence of SEQ ID NO:92; (v)VL-CDR2 has the amino acid sequence of SEQ ID NO: 153; and (vi) VL-CDR3has the amino acid sequence of SEQ ID NO:94; and wherein the proteinbinds ActRIIB and ActRIIA; (o)(i) VH-CDR1 has the amino acid sequence ofSEQ ID NO:113; (ii) VH-CDR2 has the amino acid sequence of SEQ IDNO:120; (iii) VH-CDR3 has the amino acid sequence of SEQ ID NO:121; (iv)VL-CDR1 has the amino acid sequence of SEQ ID NO:92; (v) VL-CDR2 has theamino acid sequence of SEQ ID NO: 153; and (vi) VL-CDR3 has the aminoacid sequence of SEQ ID NO:94; and wherein the protein binds ActRIIB andActRIIA; or (p)(i) VH-CDR1 has the amino acid sequence of SEQ ID NO:126;(ii) VH-CDR2 has the amino acid sequence of SEQ ID NO:127; (iii) VH-CDR3has the amino acid sequence of SEQ ID NO:128; (iv) VL-CDR1 has the aminoacid sequence of SEQ ID NO:133; (v) VL-CDR2 has the amino acid sequenceof SEQ ID NO:134; and (vi) VL-CDR3 has the amino acid sequence of SEQ IDNO:135; and wherein the protein binds ActRIIA.

In some aspects, the ActRII-binding protein specifically binds ActRIIBand comprises a set of CDRs that has a total of one, two, three, four,five, six, seven, eight, nine, ten, fewer than ten, or zero, amino acidsubstitutions, deletions, and/or insertions from a reference set of CDRsin which (i) VH-CDR1 has the amino acid sequence of SEQ ID NO:145; (ii)VH-CDR2 has the amino acid sequence of SEQ ID NO:146; (iii) VH-CDR3 hasthe amino acid sequence of SEQ ID NO:147; (iv) VL-CDR1 has the aminoacid sequence of SEQ ID NO:152; (v) VL-CDR2 has the amino acid sequenceof SEQ ID NO:153; and (vi) VL-CDR3 has the amino acid sequence of SEQ IDNO:154.

In some aspects, the ActRII-binding protein specifically binds ActIIRAand ActRIIB and comprises a set of CDRs that has a total of one, two,three, four, five, six, seven, eight, nine, ten, fewer than ten, orzero, amino acid substitutions, deletions, and/or insertions from areference set of CDRs in which (i) VH-CDR1 has the amino acid sequenceof SEQ ID NO:166; (ii) VH-CDR2 has the amino acid sequence of SEQ IDNO:167; (iii) VH-CDR3 has the amino acid sequence of SEQ ID NO:168; (iv)VL-CDR1 has the amino acid sequence of SEQ ID NO:173; (v) VL-CDR2 hasthe amino acid sequence of SEQ ID NO:174; and (vi) VL-CDR3 has the aminoacid sequence of SEQ ID NO:175.

In some aspects, the ActRII-binding protein specifically binds ActRIIand comprises a VH and a VL pair selected from the group consisting of:(a)(i) a VH having at least 90%, 95%, 97%, 98%, or 99% sequence identityto SEQ ID NO:2, 16, 22, 28, 34, or 40, and (ii) a VL having at least90%, 95%, 97%, 98%, or 99% sequence identity to SEQ ID NO:9, and whereinthe protein binds ActRIIB; (b)(i) a VH having at least 90%, 95%, 97%,98%, or 99% sequence identity to SEQ ID NO:45 or 57, and (ii) a VLhaving at least 90%, 95%, 97%, 98%, or 99% sequence identity to SEQ IDNO:50, and wherein the protein binds ActRIIB; (c)(i) a VH having atleast 90%, 95%, 97%, 98%, or 99% sequence identity to SEQ ID NO:63 or77, and (ii) a VL having at least 90%, 95%, 97%, 98%, or 99% sequenceidentity to SEQ ID NO:70, and wherein the protein binds ActRIIB; (d)(i)a VH having the amino acid sequence of SEQ ID NO:84, 98, 105, 112, or119, and (ii) a VL having the amino acid sequence of SEQ ID NO:91, andwherein the protein binds ActRIIB and ActRIIA; and (e)(i) a VH having atleast 90%, 95%, 97%, 98%, or 99% sequence identity to SEQ ID NO:125, and(ii) a VL having at least 90%, 95%, 97%, 98%, or 99% sequence identityto SEQ ID NO:132, and wherein the protein binds ActRIIA.

In some aspects, the ActRII-binding protein specifically binds ActRIIBand comprises a VH having at least 90%, 95%, 97%, 98%, or 99% sequenceidentity to SEQ ID NO:144, and a VL having at least 90%, 95%, 97%, 98%,or 99% sequence identity to SEQ ID NO:151.

In some aspects, the ActRII-binding protein specifically binds ActIIRAand ActRIIB and comprises a VH having at least 90%, 95%, 97%, 98%, or99% sequence identity to SEQ ID NO:165, and a VL having at least 90%,95%, 97%, 98%, or 99% sequence identity to SEQ ID NO:172.

In a further aspect, the ActRII-binding protein comprises a VH and a VLpair selected from the group consisting of: (a) a VH sequence of SEQ IDNO:2, 16, 22, 28, 34, or 40, and a VL sequence of SEQ ID NO:9; andwherein the protein binds ActRIIB; (b) a VH sequence of SEQ ID NO:45 or57, and a VL sequence of SEQ ID NO:50; and wherein the protein bindsActRIIB; (c) a VH sequence of SEQ ID NO:63 or 77, and a VL sequence ofSEQ ID NO:70; and wherein the protein binds ActRIIB; (d) a VH sequenceof SEQ ID NO:84, 98, 105, 112, or 119, and a VL sequence of SEQ IDNO:91; and wherein the protein binds ActRIIB and ActRIIA; and (e) a VHsequence of SEQ ID NO:125, and a VL sequence of SEQ ID NO:132 andwherein the protein binds ActRIIA.

In additional aspects an ActRII-binding protein competes for binding toActRII with an antibody comprising a VH and a VL sequence pair disclosedherein. In some aspects, an ActRII-binding protein binds to the sameepitope as an ActRII-binding protein disclosed herein.

In some aspects, the ActRII-binding protein binds a polypeptide selectedfrom the group consisting of: (a) amino acid residues NANWELERT (SEQ IDNO:157) of ActRIIB; (b) amino acid residues CCEGNFCNER (SEQ ID NO:159)of ActRIIB; (c) amino acid residues CCEGNMCNEK (SEQ ID NO:161) ofActRIIA; and (d) amino acid residues ECLFFNANWEKD (SEQ ID NO:162) ofActRIIA.

In a further aspect, the ActRII-binding protein comprises a VH sequenceof SEQ ID NO:144, and a VL sequence of SEQ ID NO:151; and the proteinbinds ActRIIB.

In a further aspect, the ActRII-binding protein comprises a VH sequenceof SEQ ID NO:165, and a VL sequence of SEQ ID NO:172; and the proteinbinds ActIIRA and ActRIIB.

In a further aspect, the ActRII-binding protein comprises a VH and a VLpair selected from the group consisting of: (a) a VH sequence of SEQ IDNO:2 and a VL sequence of SEQ ID NO:9; (b) a VH sequence of SEQ ID NO:16and a VL sequence of SEQ ID NO:9; (c) a VH sequence of SEQ ID NO:22 anda VL sequence of SEQ ID NO:9; (d) a VH sequence of SEQ ID NO:28 and a VLsequence of SEQ ID NO:9; (e) a VH sequence of SEQ ID NO:34 and a VLsequence of SEQ ID NO:9; (f) a VH sequence of SEQ ID NO:40 and a VLsequence of SEQ ID NO:9; (g) a VH sequence of SEQ ID NO:45 and a VLsequence of SEQ ID NO:50; (h) a VH sequence of SEQ ID NO:57 and a VLsequence of SEQ ID NO:50; (i) a VH sequence of SEQ ID NO:63 and a VLsequence of SEQ ID NO:70; (j) a VH sequence of SEQ ID NO:77 and a VLsequence of SEQ ID NO:70; (k) a VH sequence of SEQ ID NO:84 and a VLsequence of SEQ ID NO:91; (l) a VH sequence of SEQ ID NO:98 and a VLsequence of SEQ ID NO:91; (m) a VH sequence of SEQ ID NO:105 and a VLsequence of SEQ ID NO:91; (n) a VH sequence of SEQ ID NO:112 and a VLsequence of SEQ ID NO:91; (o) VH sequence of SEQ ID NO:119 and a VLsequence of SEQ ID NO:91; and (p) VH sequence of SEQ ID NO:125 and a VLsequence of SEQ ID NO:132. In a further aspect, the ActRII-bindingprotein comprises a VH having a sequence of SEQ ID NO:144 and a VLhaving a sequence of SEQ ID NO:151. In a further aspect, theActRII-binding protein comprises a VH having a sequence of SEQ ID NO:165and a VL having a sequence of SEQ ID NO:172.

In some aspects, the ActRII-binding protein comprises a VH and a VL pairselected from the group consisting of: (a)(i) a VH sequence having atotal of one, two, three, four, five, six, seven, eight, nine, ten,fewer than fifteen, or zero, amino acid substitutions, deletions, and/orinsertions from a reference VH sequence selected from the groupconsisting of SEQ ID NO:2, 16, 22, 28, 34, or 40, and (ii) a VL sequencehaving a total of one, two, three, four, five, six, seven, eight, nine,ten, fewer than fifteen, or zero, amino acid substitutions, deletions,and/or insertions from a reference VL sequence of SEQ ID NO:9, andwherein the protein binds ActRIIB; (b)(i) a VH sequence having a totalof one, two, three, four, five, six, seven, eight, nine, ten, fewer thanfifteen, or zero, amino acid substitutions, deletions, and/or insertionsfrom a reference VH sequence of SEQ ID NO:45 or 57, and (ii) a VLsequence having a total of one, two, three, four, five, six, seven,eight, nine, ten, fewer than fifteen, or zero, amino acid substitutions,deletions, and/or insertions from a reference VL sequence of SEQ IDNO:50, and wherein the protein binds ActRIIB; (c)(i) a VH sequencehaving a total of one, two, three, four, five, six, seven, eight, nine,ten, fewer than fifteen, or zero, amino acid substitutions, deletions,and/or insertions from a reference VH sequence of SEQ ID NO:63 or 77,and (ii) a VL sequence having a total of one, two, three, four, five,six, seven, eight, nine, ten, fewer than fifteen, or zero, amino acidsubstitutions, deletions, and/or insertions from a reference VL sequenceof SEQ ID NO:70, and wherein the protein binds ActRIIB; (d)(i) a VHsequence having a total of one, two, three, four, five, six, seven,eight, nine, ten, fewer than fifteen, or zero, amino acid substitutions,deletions, and/or insertions from a reference VH sequence selected fromthe group consisting of SEQ ID NO:84, 98, 105, 112, or 119, and (ii) aVL sequence having a total of one, two, three, four, five, six, seven,eight, nine, ten, fewer than fifteen, or zero, amino acid substitutions,deletions, and/or insertions from a reference VL sequence of SEQ IDNO:91, and wherein the protein binds ActRIIB and ActRIIA; (e)(i) a VHsequence having a total of one, two, three, four, five, six, seven,eight, nine, ten, fewer than fifteen, or zero, amino acid substitutions,deletions, and/or insertions from a reference VH sequence of SEQ IDNO:125, and (ii) a VL sequence having a total of one, two, three, four,five, six, seven, eight, nine, ten, fewer than fifteen, or zero, aminoacid substitutions, deletions, and/or insertions from a reference VL ofSEQ ID NO:132, and wherein the protein binds ActRIIA.

In some aspects, the ActRII-binding protein comprises a VH sequencehaving a total of one, two, three, four, five, six, seven, eight, nine,ten, fewer than fifteen, or zero, amino acid substitutions, deletions,and/or insertions from a reference VH sequence of SEQ ID NO:144, and aVL sequence having a total of one, two, three, four, five, six, seven,eight, nine, ten, fewer than fifteen, or zero, amino acid substitutions,deletions, and/or insertions from a reference VL sequence of SEQ IDNO:151, and the protein binds ActRIIB.

In some aspects, the ActRII-binding protein comprises a VH sequencehaving a total of one, two, three, four, five, six, seven, eight, nine,ten, fewer than fifteen, or zero, amino acid substitutions, deletions,and/or insertions from a reference VH sequence of SEQ ID NO:165, and aVL sequence having a total of one, two, three, four, five, six, seven,eight, nine, ten, fewer than fifteen, or zero, amino acid substitutions,deletions, and/or insertions from a reference VL sequence of SEQ IDNO:172, and the protein binds ActIIRA and ActRIIB.

In a further aspect, the ActRII-binding protein comprises a VH and a VLpair wherein: (a) the VH sequence has a total of one, two, three, four,five, six, seven, eight, nine, ten, fewer than fifteen, or zero, aminoacid substitutions, deletions, and/or insertions from a reference VHsequence of SEQ ID NO:2; and the VL sequence has a total of one, two,three, four, five, six, seven, eight, nine, ten, fewer than fifteen, orzero, amino acid substitutions, deletions, and/or insertions from areference VL sequence of SEQ ID NO:9; and wherein the protein bindsActRIIB; (b) the VH sequence has a total of one, two, three, four, five,six, seven, eight, nine, ten, fewer than fifteen, or zero, amino acidsubstitutions, deletions, and/or insertions from a reference VH sequenceof SEQ ID NO:16; the VL sequence has a total of one, two, three, four,five, six, seven, eight, nine, ten, fewer than fifteen, or zero, aminoacid substitutions, deletions, and/or insertions from a reference VLsequence of SEQ ID NO:9; and wherein the protein binds ActRIIB; (c) theVH sequence has a total of one, two, three, four, five, six, seven,eight, nine, ten, fewer than fifteen, or zero, amino acid substitutions,deletions, and/or insertions from a reference VH sequence of SEQ IDNO:22; and the VL sequence has a total of one, two, three, four, five,six, seven, eight, nine, ten, fewer than fifteen, or zero, amino acidsubstitutions, deletions, and/or insertions from a reference VL sequenceof SEQ ID NO:9; and wherein the protein binds ActRIIB; (d) the VHsequence has a total of one, two, three, four, five, six, seven, eight,nine, ten, fewer than fifteen, or zero, amino acid substitutions,deletions, and/or insertions from a reference VH sequence of SEQ IDNO:28; and the VL sequence has a total of one, two, three, four, five,six, seven, eight, nine, ten, fewer than fifteen, or zero, amino acidsubstitutions, deletions, and/or insertions from a reference VL sequenceof SEQ ID NO:9; and wherein the protein binds ActRIIB; (e) the VHsequence has a total of one, two, three, four, five, six, seven, eight,nine, ten, fewer than fifteen, or zero, amino acid substitutions,deletions, and/or insertions from a reference VH sequence of SEQ IDNO:34; and the VL sequence has a total of one, two, three, four, five,six, seven, eight, nine, ten, fewer than fifteen, or zero, amino acidsubstitutions, deletions, and/or insertions from a reference VL sequenceof SEQ ID NO:9; and wherein the protein binds ActRIIB; (f) the VHsequence has a total of one, two, three, four, five, six, seven, eight,nine, ten, fewer than fifteen, or zero, amino acid substitutions,deletions, and/or insertions from a reference VH sequence of SEQ IDNO:40; and the VL sequence has a total of one, two, three, four, five,six, seven, eight, nine, ten, fewer than fifteen, or zero, amino acidsubstitutions, deletions, and/or insertions from a reference VL sequenceof SEQ ID NO:9; and wherein the protein binds ActRIIB; (g) the sequencehas a total of one, two, three, four, five, six, seven, eight, nine,ten, fewer than fifteen, or zero, amino acid substitutions, deletions,and/or insertions from a reference VH sequence of SEQ ID NO:45; and theVL sequence has a total of one, two, three, four, five, six, seven,eight, nine, ten, fewer than fifteen, or zero, amino acid substitutions,deletions, and/or insertions from a reference VL sequence of SEQ IDNO:50; wherein the protein binds ActRIIB; (h) the VH sequence has atotal of one, two, three, four, five, six, seven, eight, nine, ten,fewer than fifteen, or zero, amino acid substitutions, deletions, and/orinsertions from a reference VH sequence of SEQ ID NO:57; and the VLsequence has a total of one, two, three, four, five, six, seven, eight,nine, ten, fewer than fifteen, or zero, amino acid substitutions,deletions, and/or insertions from a reference VL sequence of SEQ IDNO:50; wherein the protein binds ActRIIB; (i) the VH sequence has atotal of one, two, three, four, five, six, seven, eight, nine, ten,fewer than fifteen, or zero, amino acid substitutions, deletions, and/orinsertions from a reference VH sequence of SEQ ID NO:63; and the VLsequence has a total of one, two, three, four, five, six, seven, eight,nine, ten, fewer than fifteen, or zero, amino acid substitutions,deletions, and/or insertions from a reference VL sequence of SEQ IDNO:70; and wherein the protein binds ActRIIB; (j) the VH sequence has atotal of one, two, three, four, five, six, seven, eight, nine, ten,fewer than fifteen, or zero, amino acid substitutions, deletions, and/orinsertions from a reference VH sequence of SEQ ID NO:77; and the VLsequence has a total of one, two, three, four, five, six, seven, eight,nine, ten, fewer than fifteen, or zero, amino acid substitutions,deletions, and/or insertions from a reference VL sequence of SEQ IDNO:70; and wherein the protein binds ActRIIB; (k) the sequence has atotal of one, two, three, four, five, six, seven, eight, nine, ten,fewer than fifteen, or zero, amino acid substitutions, deletions, and/orinsertions from a reference VH sequence of SEQ ID NO:84; and the VLsequence has a total of one, two, three, four, five, six, seven, eight,nine, ten, fewer than fifteen, or zero, amino acid substitutions,deletions, and/or insertions from a reference VL sequence of SEQ IDNO:91; wherein the protein binds ActRIIB and ActRIIA; (l) the VHsequence has a total of one, two, three, four, five, six, seven, eight,nine, ten, fewer than fifteen, or zero, amino acid substitutions,deletions, and/or insertions from a reference VH sequence of SEQ IDNO:98; and the VL sequence has a total of one, two, three, four, five,six, seven, eight, nine, ten, fewer than fifteen, or zero, amino acidsubstitutions, deletions, and/or insertions from a reference VL sequenceof SEQ ID NO:91; wherein the protein binds ActRIIB and ActRIIA; (m) theVH sequence has a total of one, two, three, four, five, six, seven,eight, nine, ten, fewer than fifteen, or zero, amino acid substitutions,deletions, and/or insertions from a reference VH sequence of SEQ IDNO:105; and the VL sequence has a total of one, two, three, four, five,six, seven, eight, nine, ten, fewer than fifteen, or zero, amino acidsubstitutions, deletions, and/or insertions from a reference VL sequenceof SEQ ID NO:91; and wherein the protein binds ActRIIB and ActRIIA; (n)the VH sequence has a total of one, two, three, four, five, six, seven,eight, nine, ten, fewer than fifteen, or zero, amino acid substitutions,deletions, and/or insertions from a reference VH sequence of SEQ IDNO:112; and the VL sequence has a total of one, two, three, four, five,six, seven, eight, nine, ten, fewer than fifteen, or zero, amino acidsubstitutions, deletions, and/or insertions from a reference VL sequenceof SEQ ID NO:91; and wherein the protein binds ActRIIB and ActRIIA; (o)the VH sequence has a total of one, two, three, four, five, six, seven,eight, nine, ten, fewer than fifteen, or zero, amino acid substitutions,deletions, and/or insertions from a reference VH sequence of SEQ IDNO:119; and the VL sequence has a total of one, two, three, four, five,six, seven, eight, nine, ten, fewer than fifteen, or zero, amino acidsubstitutions, deletions, and/or insertions from a reference VL sequenceof SEQ ID NO:91; and wherein the protein binds ActRIIB and ActRIIA; or(p) the VH sequence has a total of one, two, three, four, five, six,seven, eight, nine, ten, fewer than fifteen, or zero, amino acidsubstitutions, deletions, and/or insertions from a reference VH sequenceof SEQ ID NO:125; and the VL sequence has a total of one, two, three,four, five, six, seven, eight, nine, ten, fewer than fifteen, or zero,amino acid substitutions, deletions, and/or insertions from a referenceVL sequence of SEQ ID NO:132; and wherein the protein binds ActRIIA.

In a further aspect, the ActRII-binding protein comprises a VH and a VLpair, wherein the VH sequence has a total of one, two, three, four,five, six, seven, eight, nine, ten, fewer than fifteen, or zero, aminoacid substitutions, deletions, and/or insertions from a reference VHsequence of SEQ ID NO:144, and the VL sequence has a total of one, two,three, four, five, six, seven, eight, nine, ten, fewer than fifteen, orzero, amino acid substitutions, deletions, and/or insertions from areference VL sequence of SEQ ID NO:151; and wherein the protein bindsActRIIB.

In a further aspect, the ActRII-binding protein comprises a VH and a VLpair, wherein the VH sequence has a total of one, two, three, four,five, six, seven, eight, nine, ten, fewer than fifteen, or zero, aminoacid substitutions, deletions, and/or insertions from a reference VHsequence of SEQ ID NO:165, and the VL sequence has a total of one, two,three, four, five, six, seven, eight, nine, ten, fewer than fifteen, orzero, amino acid substitutions, deletions, and/or insertions from areference VL sequence of SEQ ID NO:172; and wherein the protein bindsActRIIA and ActRIIB.

In some aspects, the ActRII-binding protein is an antibody thatspecifically binds ActRII. In additional aspects, the antibody is amonoclonal antibody, a recombinant antibody, a human antibody, ahumanized antibody, a chimeric antibody, a bi-specific antibody, or amulti-specific antibody. Some aspects, the ActRII-binding protein is theActRII-binding antibody fragment. In some aspects the antibody is anantibody fragment selected from the group consisting of a Fab, Fab′,F(ab′)₂, Fv, diabody, DART, and a single chain antibody molecule (e.g.,a BiTE).

Nucleic acids and sets of nucleic acids encoding ActRII-binding proteinsare also provided. Vectors and sets of vectors containing the nucleicacids and sets of nucleic acids, and host cells transformed with thenucleic acids and vectors are further provided. In some aspects, thehost cell is a hybridoma or mammalian host cell such as, a NS0 murinemyeloma cell, a PER.C6® human cell, or a Chinese hamster ovary (CHO)cell. Host cells including mammalian host cells and hybridomas thatproduce ActRII-binding proteins are also provided.

Methods for making an ActRII-binding protein are also provided. In someaspects, the method comprises culturing a host cell capable ofexpressing the ActRII-binding protein under suitable conditions forexpressing the protein and optionally isolating the expressedActRII-binding protein. ActRII-binding proteins prepared and/or isolatedusing methods disclosed herein or otherwise known in the art are alsoprovided.

Pharmaceutical compositions comprising an ActRII-binding protein and apharmaceutically acceptable carrier are further provided. In someaspects, the disclosure provides methods for treating and/orameliorating a condition in a subject associated with elevated ActRIIexpression or ActRII-mediated signaling. In some aspects, the methodsdecrease ActRII-mediated signaling in the subject. Also provided is theuse of an ActRII-binding protein provided herein (e.g., an anti-ActRIIB-and/or ActRIIA-binding antibody), in the manufacture or preparation of amedicament. In some embodiments, the medicament is for the treatmentand/or amelioration of a condition in a subject associated with elevatedActRII expression or ActRII-mediated signaling. In an additionalembodiment the disclosure provides the use of an ActRII-binding proteinas provided herein in the manufacture of a medicament for the treatmentof a disease or condition described herein.

Conditions that may be treated and/or ameliorated in a subject using theprovided methods include, but are not limited to: muscle disorders suchas degenerative muscle disease, muscular dystrophy, muscle atrophy, ormuscle wasting disorders; a fibrotic condition (e.g., a hepatic,pulmonary, vascular and/or ocular fibrotic condition, such as myocardialfibrosis, and idiopathic pulmonary fibrosis (IPF)); metabolic disease(e.g., type II diabetes insulin resistance, hyperglycemia, and obesity);inflammatory disease or conditions, autoimmune disease, cardiovasculardisease (e.g., congestive heart failure, and hypertension); oculardisease such as age-related macular degeneration; pulmonary disease,musculoskeletal disease, skeletal disease such as osteoporosis;neurologic disease: neuromuscular disease, degenerative disease, woundhealing; weight loss; and cancer (e.g., a carcinoma, myeloma, abone-loss inducing cancer, pituitary cancer, and gastrointestinalcancer).

In some aspects, the disclosed methods include administering apharmaceutical composition comprising an effective amount of anActRII-binding protein to a subject in need thereof. In some aspects,the ActRII-binding protein is administered alone. In other aspects, theActRII-binding protein is administered as a combination therapy. Infurther aspects, the ActRII-binding protein is administered as acombination therapy to the standard of care treatment/therapy.

Methods of blocking or reducing ActRII activity (e.g., ligand bindingand/or signaling) are also provided. In some aspects the methodcomprises contacting an ActRII-binding protein and a cell that expressesthe ActRII. In some instances the method comprises contacting anActRII-binding protein and a cell that expresses the ActRII in thepresence of an ActRII ligand (e.g., activin A). In some aspects, themethod is performed in vivo. In other aspects, the method is performedin vitro. In some aspects the blocked or reduced ActRII activity is thephosphorylation of ActRI. In further aspects, the phosphorylated ActRIis ALK4 and/or ALK7. In additional aspects the blocked or reduced ActRIIactivity is the phosphorylation of Smads (e.g., Smad2 and/or Smad3). Insome aspects, the disclosure provides a method of blocking or reducingActRII activity in a subject that comprise administering an effectiveamount of an ActRII-binding protein to a subject in need thereof. Insome aspects a method of reducing ActRIIA activity in a subject isprovided that comprises administering an effective amount of anActRIIA-binding protein to a subject in need thereof. In some aspects amethod of reducing ActRIIB activity in a subject is provided thatcomprises administering an effective amount of an ActRIIB-bindingprotein to a subject in need thereof.

Also provided is a method of blocking or reducing ActRII activity in apathological condition associated with increased ActRII expressionand/or ActRII signaling, or in a pathological condition that can betreated and/or ameliorated by reducing or inhibiting the activity of anActRII-ligand. In some instances, the method comprises administering anActRII-binding protein to a subject having increased expression ofActRII or an ActRII-ligand. In some aspects the pathological conditionis a muscle disorder. In further aspects, the muscle disorder is wastingor muscular dystrophy. In some aspects the pathological condition is ametabolic condition such as obesity or type II diabetes. In some aspectsthe pathological condition is a fibrotic condition of the lung, orliver. In additional aspects the pathological condition is a cancer. Infurther aspects, the cancer is myelofibrosis, myeloma (e.g., multiplemyeloma), pituitary cancer, breast cancer, gastrointestinal cancer, or acarcinoma. In additional aspects the pathological condition is abone-loss inducing cancer (e.g., prostate and breast cancer). In someaspects, the disclosure provides a method of blocking or reducing ActRIIactivity in a pathological condition associated with cancer treatmentinduced bone loss.

In some aspects, the disclosure provides a method of treating and/orameliorating a muscle disorder. In some instances, the method comprisesadministering an ActRII-binding protein (e.g., an anti-ActRII antibody)to a subject having a muscle disorder. Further provided is use of anActRII-binding protein as provided herein in the manufacture of amedicament for the treatment or amelioration of a muscle disorder. Infurther aspects the muscle disorder is wasting or muscular dystrophy. Inother aspects, the subject is at risk of developing a muscle disorder.In further aspects the subject is at risk of developing wasting ormuscular dystrophy.

In some aspects, the disclosure provides a method of treating and/orameliorating a fibrotic condition. In some instances, the methodcomprises administering an ActRII-binding protein (e.g., in apharmaceutical composition described herein) to a subject having afibrotic condition. In other aspects, the subject is at risk ofdeveloping a fibrotic condition. In some aspects the fibrotic conditionis chronic. Further provided is use of an ActRII-binding protein asprovided herein in the manufacture of a medicament for the treatment oramelioration of a fibrotic condition.

In some aspects, the disclosure provides a method of decreasing fibrosisin a subject. In some instances, the method comprises administering anActRII-binding protein (e.g., an anti-ActRII antibody such as afull-length ActRII-antibody or an ActRII-binding antibody fragment, andvariants and derivatives thereof) to a subject having a fibrosis. Insome aspects, the fibrosis is a hepatic or pulmonary fibrosis. Furtherprovided is use of an ActRII-binding protein as provided herein in themanufacture of a medicament for the treatment or amelioration offibrosis.

In another aspect, the disclosure provides a method of reducing the lossof hepatic or pulmonary function caused by fibrosis in a subject. Insome aspects, the method comprises administering an ActRII-bindingprotein (e.g., an anti-ActRII antibody such as a full-lengthActRII-antibody and an ActRII-binding fragment thereof) to a subject inneed thereof. In some aspects the method reduces the loss of hepaticfunction in a subject. In some aspects the method reduces the loss ofpulmonary function in a subject.

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES

FIGS. 1A-1N depict kinetic characterization of A01 lineage antibodiesbinding to hActRIIB and hActRIIA as determined by BIACORE®-basedanalysis at 37° C. Monomeric or dimeric hActRIIB or hActRIIA wascaptured on a chip and then exposed to concentrations of A01 lineageantibodies. FIGS. 1A-1D depict characterization of antibody A01 (parent)binding to ActRIIB monomer (FIG. 1A), ActRIIB dimer (FIG. 1B), ActRIIAmonomer (FIG. 1C), and ActRIIA dimer (FIG. 1D). FIGS. 1E and 1F depictcharacterization of antibody B01 binding to ActRIIB monomer (FIG. 1E)and ActRIIB dimer (FIG. 1F). FIGS. 1G-1H depict antibody C01 binding toActRIIB monomer (FIG. 1G) and ActRIIB dimer (FIG. 1H). FIGS. 1I-1Jdepict antibody D01 binding to ActRIIB monomer (FIG. 1I) and ActRIIBdimer (FIG. 1J). FIGS. 1K-1L depict antibody E01 binding to ActRIIBmonomer (FIG. 1K) and ActRIIB dimer (FIG. 1L). FIGS. 1M-1N depictantibody F01 binding to ActRIIB monomer (FIG. 1M) and ActRIIB dimer(FIG. 1N).

FIG. 2 depicts neutralizing activity of A01 lineage antibodies in acell-based reporter gene assay. Included are assay responses withactivin A alone (2 ng/ml), and activin A, combined with 50 ng/ml of A01lineage antibodies A01, B01, C01, D01, E01, and F01.

FIGS. 3A-3F depict kinetic characterization of G02 lineage antibodiesbinding to hActRIIB and hActRIIA as determined by BIACORE®-basedanalysis at 37° C. Monomeric or dimeric hActRIIB or hActRIIA wascaptured on a chip and then exposed G01 lineage. FIGS. 3A-3D depictcharacterization of antibody G01 binding to ActRIIB monomer (FIG. 3A),ActRIIB dimer (FIG. 3B), ActRIIA monomer (FIG. 3C), and ActRIIA dimer(FIG. 3D). FIGS. 1E and 1F depict characterization of antibody H01binding to ActRIIB monomer (FIG. 3E) and ActRIIB dimer (FIG. 3F).

FIG. 4 depicts neutralizing activity of G01 parent and H01 optimizedantibodies in a cell-based reporter gene assay. Included are assayresponses in the absence of activin A, with activin A alone (2 ng/ml),and activin A, combined with 50 ng/ml of G01 lineage antibodies G01 orH01.

FIGS. 5A-5P depict kinetic characterization of A02 lineage antibodiesbinding to hActRIIB and hActRIIA as determined by BIACORE®-basedanalysis at 37° C. Monomeric or dimeric hActRIIB or hActRIIA wascaptured on a chip with and then exposed to A02 lineage antibodies.FIGS. 5A-5D depict characterization of antibody A02 (parent) binding toActRIIB monomer (FIG. 5A), ActRIIB dimer (FIG. 5B), ActRIIA monomer(FIG. 5C), and ActRIIA dimer (FIG. 5D). FIGS. 5E-5H depictcharacterization of antibody B02 binding to ActRIIB monomer (FIG. 5E),ActRIIB dimer (FIG. 5F), ActRIIA monomer (FIG. 5G), and ActRIIA dimer(FIG. 5H). FIGS. 5I-5L depict characterization of antibody C02 bindingto ActRIIB monomer (FIG. 5I), ActRIIB dimer (FIG. 5J), ActRIIA monomer(FIG. 5K), and ActRIIA dimer (FIG. 5L). FIGS. 5M-5P depictcharacterization of antibody D02 binding to ActRIIB monomer (FIG. 5M),ActRIIB dimer (FIG. 5N), ActRIIA monomer (FIG. 5O), and ActRIIA dimer(FIG. 5P). FIGS. 5Q-5T depict characterization of antibody D03 bindingto ActRIIB monomer (FIG. 5Q), ActRIIB dimer (FIG. 5R), ActRIIA monomer(FIG. 5S), and ActRIIA dimer (FIG. 5T).

FIGS. 6A-6B depict neutralizing activity of A02 lineage antibodies in acell-based reporter gene assay. Included are assay responses in theabsence of activin A, with activin A alone (2 ng/ml), and activin A,combined with 50 ng/ml of A02 lineage antibodies. FIG. 6A depictsneutralizing activity of A02 (parent), B02, C02, and D02. FIG. 6Bdepicts neutralizing activity of D02 and D03.

FIGS. 7A-7F depict kinetic characterization of E02 parent and F02variant antibody binding to hActRIIB and hActRIIA as determined byBIACORE®-based analysis at 37° C. Monomeric or dimeric hActRIIB orhActRIIA was captured on a chip and then exposed to E02 and F02. FIGS.7A-7D depict characterization of E02 parent binding to ActRIIB monomer(FIG. 7A), ActRIIB dimer (FIG. 7B), ActRIIA monomer (FIG. 7C), andActRIIA dimer (FIG. 7D). FIGS. 7E AND 7F depict characterization ofantibody F02 binding to ActRIIB monomer (FIG. 7E), and ActRIIB dimer(FIG. 7F).

FIGS. 8A-8D depict kinetic characterization of antibody G02 binding tohActRIIB and hActRIIA as determined by BIACORE®-based analysis at 37° C.Monomeric or dimeric hActRIIB or hActRIIA was captured on a chip withand then exposed to the evaluated anti-hActRII antibodies. FIGS. 8A-8Ddepict characterization of antibody G02 binding to ActRIIB monomer (FIG.8A), ActRIIB dimer (FIG. 8B), ActRIIA monomer (FIG. 8C), and ActRIIAdimer (FIG. 8D).

FIG. 9 depicts neutralizing activity of ActRIIB-binding E02 parent andF02 variant antibodies and ActRIIA-binding antibody G02 in a cell-basedreporter gene assay. Included are assay responses in the absence ofactivin A, with activin A alone (2 ng/ml), and activin A, combined with50 ng/ml of antibody E02, F02, or G02.

DETAILED DESCRIPTION

The disclosure provides isolated recombinant ActRII-binding proteins. Incertain aspects the ActRII-binding proteins specifically bind ActRIIBand/or ActRIIA. In further aspects, the ActRII-binding proteins areanti-ActRII antibodies. Nucleic acids encoding the ActRII-bindingproteins, vectors and host cells containing the nucleic acids, andmethods of making and using the ActRII-binding proteins are alsoprovided. The provided ActRII-binding proteins have uses in diagnosing,treating, and/or ameliorating diseases and conditions associated withincreased ActRII expression and/or signaling. Such uses include but arenot limited to, preventing, and/or ameliorating muscle disorders such asdegenerative muscle disease muscular dystrophy, muscle atrophy or musclewasting disorders; a fibrotic condition (e.g., a hepatic, pulmonary,vascular and/or ocular fibrotic condition, such as myocardial fibrosis,and idiopathic pulmonary fibrosis (IPF)); metabolic disease (e.g., typeII diabetes and obesity); inflammatory disease or conditions, autoimmunedisease, cardiovascular disease (e.g., congestive heart failure, andhypertension); ocular disease such as age-related macular degeneration;pulmonary disease, musculoskeletal disease, skeletal disease, neurologicdisease, such as osteoporosis; wound healing; weight loss; and cancer(e.g., a carcinoma, myeloma, a bone-loss inducing cancer, pituitarycancer, and gastrointestinal cancer).

Definitions

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this disclosure is related. For example, the ConciseDictionary of Biomedicine and Molecular Biology, Juo, Pei-Show, 2nd ed.,2002, CRC Press; The Dictionary of Cell and Molecular Biology, 3rd ed.,1999, Academic Press; and the Oxford Dictionary Of Biochemistry AndMolecular Biology, Revised, 2000, Oxford University Press, provide oneof skill with a general dictionary of many of the terms used in thisdisclosure. The headings provided herein are not limitations of thevarious aspects which can be had by reference to the specification as awhole. Moreover, the terms defined immediately below are more fullydefined by reference to the specification in its entirety.

The terms “a,” “an” and “the” include plural referents unless thecontext in which the term is used clearly dictates otherwise. The terms“a” (or “an”), as well as the terms “one or more,” and “at least one”can be used interchangeably herein. Furthermore, “and/or” where usedherein is to be taken as specific disclosure of each of the two or morespecified features or components with or without the other. Thus, theterm “and/or” as used in a phrase such as “A and/or B” herein isintended to include “A and B,” “A or B,” “A” (alone), and “B” (alone).Likewise, the term “and/or” as used in a phrase such as “A, B, and/or C”is intended to encompass each of the following aspects: A, B, and C; A,B, or C; A or C; A or B; B or C; A and C; A and B; B and C; A (alone); B(alone); and C (alone).

The term “comprise” is generally used in the sense of include, that isto say permitting the presence of one or more features or components.Wherever aspects are described herein with the language “comprising,”otherwise analogous aspects described in terms of “consisting of,”and/or “consisting essentially of” are also provided.

The terms “about” and “approximately” as used in connection with anumerical value throughout the specification and the claims denotes aninterval of accuracy, familiar and acceptable to a person skilled in theart. In general, such interval of accuracy is ±10%. Alternatively, andparticularly in biological systems, the terms “about” and“approximately” may mean values that are within an order of magnitude,preferably ≤5-fold and more preferably ≤2-fold of a given value.

Numeric ranges are inclusive of the numbers defining the range.

An ActRII-binding protein refers to a protein that specifically binds toActRII (i.e., ActRIIB and/or ActRIIA), preferrably binding to theextracellular domain of ActRII.

The terms “ActRII activin receptor type II, and “ActRII” are usedinterchangeably and refer to the activin receptor type IIA (ActRIIA)and/or activin receptor type IIB (ActRIIB) unless the context in whichthe term is used clearly dictates otherwise.

The terms “activin receptor type IIA,” “ActRIIA receptor,” and “ActRIIA”are used interchangeably herein, and refer to ActRIIA (also referred toas ACVR2A, ActRIIA, ActRII, and EC 2.7.11.30 in the literature).Reference sequence for human ActRIIA is provided in RefSeqNO:NP_001607.1. The provided ActRIIA-binding proteins bind theextracellular domain of ActRIIA corresponding to the amino acid sequenceof SEQ ID NO:138.

The terms “activin receptor type IIB,” “ActRIIB receptor,” and “ActRIIB”are used interchangeably and refer to ActRIIB (also referred to asACVR2B, ActRIIB, HTX4, ErbB3 receptor, and EC 2.7.11.30 in theliterature). Reference sequence for human ActRIIB is provided in NCBIReference Sequence NP_001097. The provided ActRIIB-binding proteins bindthe extracellular domain of ActRIIB corresponding to the amino acidsequence of SEQ ID NO:139.

The term “compete” or “competes” when used in the context ofActRII-binding proteins (e.g., neutralizing antibodies) meanscompetition between antigen binding proteins as determined by an assayin which the antigen binding protein (e.g., an anti-ActRII antibody oran ActRII-binding fragment thereof) under test prevents or inhibitsspecific binding of a reference antigen binding protein (e.g., a ligand,or a reference antibody) to a common antigen (e.g., an ActRIIA orActRIIB extracellular domain or a fragment thereof). Numerous types ofcompetitive binding assays can be used, for example: solid phase director indirect radioimmunoassay (RIA) (see, e.g., Moldenhauer et al.,Scand. J. Immunol. 32:77-82 (1990) and Morel et al., Molec. Immunol.25:7-15 (1988)), solid phase direct or indirect enzyme immunoassay(EIA), solid phase direct biotin-avidin EIA (see, e.g., Cheung, et al.,Virology 176:546-552 (1990) and Kirkland et al., J. Immunol.137:3614-3619 (1986)) and a sandwich competition assay (see, e.g.,Stahli et al., Methods in Enzymology 92:242-253 (1983)). Typically, suchan assay involves the use of purified antigen bound to a solid surfaceor cells bearing either of these, an unlabeled test antigen bindingprotein and a labeled reference antigen binding protein.

Competitive inhibition can be measured by determining the amount oflabel bound to the solid surface or cells in the presence of the testantigen binding protein. Usually the test antigen binding protein ispresent in excess. Antigen binding proteins identified by competitionassay (competing antigen binding proteins) include ActRII-bindingproteins that bind to the same epitope as the reference ActRII-bindingprotein as well as ActRII-binding proteins that bind to an adjacentepitope sufficiently proximal to the epitope bound by the referenceActRII-binding protein for steric hindrance to occur. Usually, when acompeting ActRII (e.g., ActRIIA or ActRIIB) binding protein is presentin excess, it will inhibit specific binding of a referenceActRII-binding protein ActRII (e.g., ActRIIA or ActRIIB) by at least40%, 45%, 50%, 55%, 60%, 65%, 70% or 75%. In some instance, a competingantigen binding protein inhibits specific binding of a referenceActRII-binding protein by at least 80%, 85%, 90%, 91%, 92%, 93%, 94%,95%, 96%, 97% 98%, or 99%.

The term “epitope” when used in context of an ActRII protein refers toan ActRII (e.g., human ActRIIA, human ActRIIB, murine ActRIIA or murineActRIIA) protein determinant capable of binding to an ActRII-bindingprotein (e.g., an antibody) of the disclosure. Epitopes usually consistof chemically active surface groupings of molecules such as amino acidsor sugar side chains and usually have specific three-dimensionalstructural characteristics, as well as specific charge characteristics.Conformational and non-conformational epitopes are distinguished in thatthe binding to the former but not the latter is lost in the presence ofdenaturing solvents. The ActRII epitope bound by an ActRII-bindingprotein can readily be determined using techniques known in the art.

Antigen binding proteins such as the anti-ActRII-binding antibodies andActRII-binding binding fragments, variants, or derivatives thereofdisclosed herein, can be described or specified in terms of theepitope(s) or portion(s) of an antigen, e.g., a target polypeptide thatthey recognize or specifically bind. For example, the portion of ActRIIthat specifically interacts with the antigen binding domain of anActRII-binding protein disclosed herein is an “epitope.” Epitopes can beformed both from contiguous amino acids or noncontiguous amino acidsjuxtaposed by tertiary folding of a protein. Epitopes formed fromcontiguous amino acids are typically retained on exposure to denaturingsolvents, whereas epitopes formed by tertiary folding are typically loston treatment with denaturing solvents. Epitope determinants may includechemically active surface groupings of molecules such as amino acids,sugar side chains, phosphoryl or sulfonyl groups, and may have specificthree dimensional structural characteristics, and/or specific chargecharacteristics. An epitope typically includes at least 3, 4, 5, 6, 3,4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 25, 30, 35amino acids in a unique spatial conformation. Epitopes can routinely bedetermined using methods known in the art.

The terms “inhibit,” “block,” “reduce,” “decrease,” “suppress,”“antagonize,” and “neutralize” are used interchangeably and refer to anystatistically significant decrease in activity (e.g., ActRII ligandbinding and ActRII signaling), including full blocking of the activity.For example, “inhibition” or “suppression” can refer to a decrease ofabout 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or 100% in activitycompared to a control.

In some aspects, the term “decrease” may refer to the ability of anActRII-binding protein such as an antibody or ActRII-binding fragmentthereof, to statistically significantly (e.g., with a p value less thanor equal to 0.05) decrease the phosphorylation of one or more Smads(e.g., Smad2 and/or Smad3) induced by contacting a cell expressingActRII and a type I receptor with an ActRII ligand such as activin A,relative to the extent of Smad phosphorylation in the cell when notcontacted with the ActRII-binding protein. The cell which expressesActRII (e.g., ActRIIB and/or ActRIIA) can be a naturally occurring cellor a cell line, or can be recombinantly produced by introducing anucleic acid encoding ActRII (e.g., ActRIIB and/or ActRIIA) into a hostcell. In one aspect, the ActRII-binding protein, e.g., an ActRIIantibody or ActRII-binding fragment thereof, decreases ActRII ligandmediated phosphorylation of one or more Smads (e.g., Smad2 and/or Smad3)by at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 95%, or byabout 100%, as determined, for example, by Western blotting followed byprobing with an anti-phosphotyrosine antibody or by ELISA, usingstandard techniques and conditions described herein or otherwise knownin the art.

In some aspects, an ActRIIA-binding protein decreases ActRIIA ligand(e.g., activin A) mediated phosphorylation of one or more Smads (e.g.,Smad2 and/or Smad3) by at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%,90%, or 95%, or by about 100%, as determined, for example, by Westernblotting followed by probing with an anti-phosphotyrosine antibody or byELISA (e.g., P-Smad ELISA) or a Smad dependent reporter gene assay usingtechniques described herein or otherwise known in the art.

In additional aspects, an ActRIIB-binding protein decreases ActRIIBligand (e.g., activin A or GDF8)-mediated phosphorylation of one or moreSmads (e.g., Smad2 and/or Smad3) by at least 10%, 20%, 30%, 40%, 50%,60%, 70%, 80%, 90%, or 95%, or by about 100%, as determined, forexample, by Western blotting followed by probing with ananti-phosphotyrosine antibody or by ELISA (e.g., a P-Smad ELISA) or aSmad dependent reporter gene assay using standard techniques andconditions described herein or otherwise known in the art.

The terms “antibody” and “immunoglobulin,” are used interchangeablyherein, and include whole (full-length) antibodies and antigen bindingfragment or single chains thereof. A typical antibody comprises at leasttwo heavy (H) chains and two light (L) chains interconnected bydisulfide bonds. Each heavy chain is comprised of a heavy chain variableregion (abbreviated herein as VH) and a heavy chain constant region. Theheavy chain constant region is comprised of three domains, CHI, CH2, andCH3. Each light chain is comprised of a light chain variable region(abbreviated herein as VL) and a light chain constant region. The lightchain constant region is comprised of one domain, CL. The VH and VLregions can be further subdivided into regions of hypervariability,termed Complementarity Determining Regions (CDR), interspersed withregions that are more conserved, termed framework regions (FW). Each VHand VL is composed of three CDRs and four FWs, arranged fromamino-terminus to carboxy-terminus in the following order: FW1, CDR1,FW2, CDR2, FW3, CDR3, FW4. The variable regions of the heavy and lightchains contain a binding domain that interacts with an antigen. Theconstant regions of the antibodies can mediate the binding of theimmunoglobulin to host tissues or factors, including various cells ofthe immune system (e.g., effector cells) and the first component (C1q)of the classical complement system. Exemplary antibodies include typicalantibodies, scFvs, and combinations thereof where, for example, an scFvis covalently linked (for example, via peptidic bonds or via a chemicallinker) to the N or C-terminus of either the heavy chain and/or thelight chain of a typical antibody, or intercalated in the heavy chainand/or the light chain of a typical antibody.

The terms “antibody” and “immunoglobulin,” encompass intact polyclonalantibodies, intact monoclonal antibodies, antibody fragments (such asFab, Fab′, F(ab′)2, and Fv fragments), single chain Fv (scFv)derivatives and mutants, multispecific antibodies such as bispecificantibodies, chimeric antibodies, humanized antibodies, human antibodies,fusion proteins comprising an antigen determination portion of anantibody, and any other modified immunoglobulin molecule comprising anantigen recognition site so long as the antibodies exhibit the desiredbinding activity. An antibody can be of any the five major classes ofimmunoglobulins: IgA, IgD, IgE, IgG, and IgM, or subclasses (isotypes)thereof (e.g., IgG1, IgG2, IgG3, IgG4, IgA1 and IgA2), based on theidentity of their heavy-chain constant domains referred to as alpha,delta, epsilon, gamma, and mu, respectively. The different classes ofimmunoglobulins have different and well known subunit structures andthree-dimensional configurations. Antibodies can be naked or conjugatedto other molecules such as toxins, radioisotopes, etc. The term “IgG”refers to a polypeptide belonging to the class of antibodies that aresubstantially encoded by a recognized immunoglobulin gamma gene. Inhumans this class comprises IgG1, IgG2, IgG3, and IgG4. In mice thisclass comprises IgG1, IgG2a, IgG2b, and IgG3.

The terms “ActRII antibody,” “an antibody that binds to ActRII,” or“anti-ActRII antibody” refer to an antibody that is capable of bindingActRII (e.g., ActRIIB and/or ActRIIA) with sufficient affinity such thatthe antibody is useful as a therapeutic agent or diagnostic reagent intargeting ActRIIB and/or ActRIIA, respectively.

By “specifically binds” when used in the context of ActRII proteins, itis generally meant the ability of a binding protein such as an antibody,to bind to ActRII (e.g., ActRIIB and/or ActRIIA, preferably humanActRIIA and/or human ActRIIB, preferably an extracellular domain ofActRIIB and/or ActRIIA), with greater affinity than the binding proteinbinds to an unrelated control protein. In some aspects, the controlprotein is hen egg white lysozyme. Preferably the binding protein bindsActRII with an affinity that is at least, 100, 500, or 1000 timesgreater than the affinity for a control protein. Preferably, the bindingprotein has a binding affinity for human ActRII of ≤1×10⁻⁷ M or ≤1×10⁻⁸as measured using a binding assay known in the art. In some aspects, thebinding affinity is measured using a radioimmunoassay (RIA) or BIACORE®(e.g., using ActRII (e.g., ActRIIB and/or ActRIIA) as the analyte andActRII-binding protein as the ligand, or vice versa).

In some aspects, the extent of binding of an ActRII-binding protein(e.g., an anti-ActRII antibody) to an unrelated, non-ActRII protein isless than about 10% of the binding of the ActRII-binding protein toActRII as measured, for example, by a radioimmunoassay (RIA), BIACORE®(using recombinant ActRII as the analyte and ActRII-binding protein asthe ligand, or vice versa), kinetic exclusion assay (KINEXA®), or otherbinding assays known in the art. In certain aspects, the ActRII-bindingprotein is a full-length antibody or an ActRII-binding antibody fragmentthat has a dissociation constant (K_(D)) of ≤1 μM, ≤100 nM, ≤10 nM, ≤1nM, ≤0.1 nM, ≤10 pM, ≤1 pM, or ≤0.1 pM.

The terms “antigen binding antibody fragment” (e.g., “ActRII-bindingantibody fragment,” “ActRIIA-binding antibody fragment” and“ActRIIB-binding antibody fragment”) refer to a fragment containing allor a portion of an antigen binding variable region (e.g., CDR3) of anintact antibody. It is known that the antigen binding function of anantibody can be performed by fragments of a full-length antibody.Examples of antibody fragments include, but are not limited to Fab,Fab′, F(ab′)2, and Fv fragments, linear antibodies, single chainantibodies, and multispecific antibodies formed from one or moreantibody fragments. In some aspects the disclosure providesActRII-binding antibody fragments wherein the antibody fragment is a Fabfragment, a Fab′ fragment, a F(ab′)₂ fragment, a Fv fragment, a diabody,or a single chain antibody molecule.

The Fc region includes polypeptides comprising the constant region of anantibody excluding the first constant region immunoglobulin domain.Thus, Fc refers to the last two constant region immunoglobulin domainsof IgA, IgD, and IgG, and the last three constant region immunoglobulindomains of IgE and IgM, and the flexible hinge N-terminal to thesedomains. For IgA and IgM Fc may include the J chain. For IgG, Fccomprises immunoglobulin domains Cγ2 and Cγ3 and the hinge between Cγ1and Cγ2. Although the boundaries of the Fc region may vary, the humanIgG heavy chain Fc region is usually defined to comprise residues C226or P230 to its carboxyl-terminus, wherein the numbering is according tothe EU index as set forth in Kabat (Kabat et al., Sequences of Proteinsof Immunological Interest, 5th Ed. Public Health Service, NIH, Bethesda,Md. (1991)). Fc may refer to this region in isolation, or this region inthe context of a whole antibody, antibody fragment, or Fc fusionprotein. Polymorphisms have been observed at a number of different Fcpositions, including but not limited to positions 270, 272, 312, 315,356, and 358 as numbered by the EU index, and thus slight differencesbetween the presented sequence and sequences in the prior art may exist.

A “monoclonal antibody” refers to a homogeneous antibody populationinvolved in the highly specific recognition and binding of a singleantigenic determinant or epitope. This is in contrast to polyclonalantibodies that typically include different antibodies directed againstdifferent antigenic determinants. The term “monoclonal antibody”encompasses both intact and full-length monoclonal antibodies as well asantibody fragments (such as Fab, Fab′, F(ab′)2, and Fv), single chain(scFv) mutants, and fusion proteins) comprising an antibody portion, andany other modified immunoglobulin molecule comprising an antigenrecognition site. A monoclonal antibody may be made in any number ofways including, but not limited to, by hybridoma, phage selection,recombinant expression, and transgenic animals.

The term “chimeric antibody” refers to an antibody wherein the aminoacid sequence of the immunoglobulin molecule is derived from two or morespecies. Typically, the variable region of both light and heavy chainscorresponds to the variable region of antibodies derived from onespecies of mammal (e.g., mouse, rat, rabbit, etc.) with the desiredantigen-binding specificity, affinity, and/or capability while theconstant regions are homologous to the sequences in antibodies derivedfrom another species (usually human) to avoid eliciting an immuneresponse in that species.

The term “humanized antibody” refers to an antibody derived from anon-human (e.g., murine) immunoglobulin, which has been engineered tocontain fewer preferably minimal non-human (e.g., murine) sequences.Typically, humanized antibodies are human immunoglobulins in whichresidues from the CDR are replaced by residues from the CDR of anon-human species (e.g., mouse, rat, rabbit, or hamster) that have thedesired antigen-binding specificity, affinity, and/or capability (Jones,Nature 321:522-525 (1986); Riechmann, Nature 332:323-327 (1988);Verhoeyen, Science 239:1534-1536 (1988)). In some instances, the Fvframework region (FW) residues of a human immunoglobulin are replacedwith the corresponding residues in an antibody from a non-human speciesthat has the desired antigen-binding specificity, affinity, and/orcapability. The humanized antibody can be further modified by thesubstitution of additional residues either in the Fv framework regionand/or within the replaced non-human residues to refine and optimizeantibody specificity, affinity, and/or capability. In general, thehumanized antibody will comprise substantially all of at least one, andtypically two or three, variable domains containing all or substantiallyall of the CDR regions that correspond to the non-human immunoglobulinwhereas all or substantially all of the FR regions are those of a humanimmunoglobulin consensus sequence. The humanized antibody can alsocomprise at least a portion of an immunoglobulin constant region ordomain (Fc), typically that of a human immunoglobulin. Examples ofmethods used to generate humanized antibodies are described in U.S. Pat.Nos. 5,225,539 and 5,639,641.

The term “human antibody” refers to an antibody produced by a human oran antibody having an amino acid sequence corresponding to an antibodyproduced by a human made using any technique known in the art. The term“human antibody” includes intact (full-length) antibodies, fragmentsthereof, and/or antibodies comprising at least one human heavy and/orlight chain polypeptide such as, an antibody comprising murine lightchain and human heavy chain polypeptides.

An “antagonist,” “blocking,” or “neutralizing” binding protein is onethat inhibits or reduces activity of the antigen it binds, such asActRIIB and/or ActRIIA. In some aspects, the antagonist ActRII-bindingprotein reduces or inhibits the binding to ActRIIA by an ActRIIA ligandsuch as activin A. In some aspects, the antagonist ActRII-bindingprotein reduces or inhibits the binding to ActRIIB by an ActRIIB ligandsuch as activin A. In certain aspects the antagonist ActRII-bindingprotein substantially or completely inhibits the activity of the ActRII.In some aspects, the ActRII activity is reduced by 10%, 20%, 30%, 50%,70%, 80%, 90%, 95%, or 100%. In certain aspects the antagonistActRII-binding protein is an anti-ActRIIA antibody, such as afull-length antibody or an ActRIIA-binding antibody fragment. In furtheraspects, the antagonist anti-ActRIIA antibody inhibits or reduces theactivity of ActRIIA by at least 10%, 20%, 30%, 50%, 70%, 80%, 90%, 95%,or even 100%. In additional aspects, the antagonist ActRII-bindingprotein is an anti-ActRIIB antibody, such as a full-length antibody oran ActRIIB-binding antibody fragment. In further aspects, the antagonistanti-ActRIIB antibody inhibits or reduces the activity of ActRIIB by atleast 10%, 20%, 30%, 50%, 70%, 80%, 90%, 95%, or even 100%.

“Binding affinity” generally refers to the strength of the sum total ofnon-covalent interactions between a single binding site of a molecule(e.g., an antibody) and its binding partner (e.g., an antigen). Unlessindicated otherwise, “binding affinity” refers to intrinsic bindingaffinity which reflects a 1:1 interaction between members of a bindingpair (e.g., antibody and antigen). The affinity of a molecule X for itspartner Y can generally be represented by the dissociation constant(K_(D)). Affinity can be measured by common methods known in the art,including those described herein and can be used for the purposes of thepresent disclosure.

“Potency” is a measure of pharmacological activity of a compoundexpressed in terms of the amount of the compound required to produce aneffect of given intensity. It refers to the amount of the compoundrequired to achieve a defined biological effect; the smaller the doserequired, the more potent the drug. Potency is normally expressed as anIC₅₀ value, in nM unless otherwise stated. IC₅₀ is the median inhibitoryconcentration of an ActRII-binding protein (e.g., an anti-ActRIIA oranti-ActRIIB antibody). In functional assays, IC₅₀ is the concentrationthat reduces a biological response by 50% of its maximum. Inligand-receptor binding studies, IC₅₀ is the concentration that reducesligand-receptor binding by 50% of maximal specific binding level. IC₅₀can be calculated by any number of means known in the art. The foldimprovement in potency for the antibodies or other binding proteinprovided herein as compared to a reference anti-ActRII antibody or otherActRII-binding protein can be at least 2-fold, 4-fold, 6-fold, 8-fold,10-fold, 20-fold, 30-fold, 40-fold, 50-fold, 60-fold, 70-fold, 80-fold,90-fold, 100-fold, 110-fold, 120-fold, 130-fold, 140-fold, 150-fold,160-fold, 170-fold, or at least 180-fold.

“Antibody-dependent cell-mediated cytotoxicity” or “ADCC” refers to aform of cytotoxicity in which secreted Ig bound onto Fc receptors (FcRs)present on certain cytotoxic cells (e.g., Natural Killer (NK) cells,neutrophils, and macrophages) enables these cytotoxic effector cells tobind specifically to an antigen-bearing target cell and subsequentlykill the target cell with cytotoxins. Specific high-affinity IgGantibodies directed to the surface of target cells “arm” the cytotoxiccells and are absolutely required for such killing. Lysis of the targetcell is extracellular, requires direct cell-to-cell contact, and doesnot involve complement. It is contemplated that, in addition toantibodies, other proteins comprising Fc regions, specifically Fc fusionproteins, having the capacity to specifically bind to an ActRII-bearingtarget cell will be able to effect cell-mediated cytotoxicity. Forsimplicity, the cell-mediated cytotoxicity resulting from the activityof an Fc fusion protein is also referred to herein as ADCC activity.

An ActRII-binding protein (e.g., an ActRII antibody, including anActRII-binding fragment, variant, and derivative thereof),polynucleotide, vector, cell, or composition which is “isolated” is aprotein (e.g., antibody), polynucleotide, vector, cell, or compositionwhich is in a form not found in nature. Isolated proteins,polynucleotides, vectors, cells or compositions include those which havebeen purified to a degree that they are no longer in a form in whichthey are found in nature. In some aspects, a protein, polynucleotide,vector, cell, or composition which is isolated is substantially pure.Isolated proteins and isolated nucleic acid will be free orsubstantially free of material with which they are naturally associatedsuch as other polypeptides or nucleic acids with which they are found intheir natural environment, or the environment in which they are prepared(e.g., cell culture) when such preparation is by recombinant DNAtechnology practiced in vitro or in vivo. Proteins and nucleic acid maybe formulated with diluents or adjuvants and still for practicalpurposes be isolated—for example the proteins will normally be mixedwith gelatin or other carriers if used to coat microtitre plates for usein immunoassays, or will be mixed with pharmaceutically acceptablecarriers or diluents when used in diagnosis or therapy.

The terms “subject,” “individual,” “animal,” “patient,” and “mammal,”refer to any subject, particularly a mammalian subject, for whomdiagnosis, prognosis, or therapy is desired. Mammalian subjects includebut are not limited to humans, non-human primates, domestic animals,farm animals, rodents, and the like, which is to be the recipient of aparticular treatment.

The term “pharmaceutical composition” refers to a preparation which isin such form as to permit the biological activity of the activeingredient to be effective, and which contains no additional componentsat concentrations that are unacceptably toxic to a subject to which thecomposition would be administered. Such composition can be sterile.

An “effective amount” of a polypeptide, e.g., an antigen binding proteinincluding an antibody, as disclosed herein is an amount sufficient tocarry out a specifically stated purpose. An “effective amount” can bedetermined empirically and in a routine manner, in relation to thestated purpose. The term “therapeutically effective amount” refers to anamount of a polypeptide, e.g., an antigen binding protein including anantibody, or other drug effective to “treat” a disease or condition in asubject (e.g., a mammal such as a human) and provides some improvementor benefit to a subject having the disease or condition. Thus, a“therapeutically effective” amount is an amount that provides somealleviation, mitigation, and/or decrease in at least one clinicalsymptom of the ActRII-mediated disease or condition. Clinical symptomsassociated with the diseases or conditions that can be treated by themethods of the disclosure are well known. Further, therapeutic effectsneed not be complete or curative, as long as some benefit is provided tothe subject. In some embodiments, the term “therapeutically effective”refers to an amount of a therapeutic agent that is capable of reducingActRII activity in a patient in need thereof. The actual amountadministered and rate and time-course of administration, will depend onthe nature and severity of what is being treated. Prescription oftreatment, e.g., decisions on dosage etc., is within the responsibilityof general practitioners and other medical doctors. Appropriate doses ofantibodies and antigen binding fragments thereof are are generallyknown; see, Ledermann et al., Int. J. Cancer 47:659-664 (1991); Bagshaweet al., Ant. Immun. and Radiopharm. 4:915-922 (1991).

A “sufficient amount” or “an amount sufficient to” achieve a particularresult in a patient having an ActRII-mediated disease or conditionrefers to an amount of a therapeutic agent (e.g., an antigen bindingprotein including an antibody, as disclosed herein) that is effective toproduce a desired effect, which is optionally a therapeutic effect(i.e., by administration of a therapeutically effective amount). In someembodiments, such particular result is a reduction in ActRII activity ina patient in need thereof.

The term “label” refers to a detectable compound or composition which isconjugated directly or indirectly to a moiety such as an anti-ActRIIantibody so as to generate a “labeled” moiety. The label can bedetectable by itself (e.g., radioisotope labels or fluorescent labels)or, in the case of an enzymatic label, can catalyze chemical alterationof a substrate compound or composition which is detectable.

Terms such as “treating,” or “treatment,” “to treat” or “ameliorating”and “to ameliorate” refer to both (a) therapeutic measures that cure,slow down, lessen symptoms of, and/or halt progression of a diagnosedpathologic condition or disorder and (b) prophylactic or preventativemeasures that prevent and/or slow the development of a targeted diseaseor condition. Thus, subjects in need of treatment include those alreadywith the disease or condition; those at risk of developing the diseaseor condition; and those in whom the disease or condition is to beprevented. In certain aspects, a subject is successfully “treated”according to the methods provided herein if the subject shows, e.g.,total, partial, or transient amelioration or elimination of a symptomassociated with the disease or condition. In some aspects, thedisclosure provides a method for treating a muscle disorder, such asmuscle wasting due to disease or disuse. In additional aspects thedisclosure provides a method for treating a disease or conditionselected from muscle disorders such as degenerative muscle disease,muscular dystrophy, muscle atrophy, or muscle wasting disorders; afibrotic condition (e.g., a hepatic, pulmonary, vascular and/or ocularfibrotic condition, such as myocardial fibrosis, and idiopathicpulmonary fibrosis (IPF)); metabolic disease (e.g., type II diabetes andobesity); inflammatory disease or conditions, autoimmune disease,cardiovascular disease (e.g., congestive heart failure, andhypertension); ocular disease such as age-related macular degeneration;pulmonary disease, musculoskeletal disease, skeletal disease, neurologicdisease, such as osteoporosis; wound healing; weight loss; and cancer(e.g., a carcinoma, myeloma, a bone-loss inducing cancer, pituitarycancer, and gastrointestinal cancer). In further aspects the disclosureprovides use of an ActRII-binding protein as provided herein in themanufacture of a medicament for the treatment or amelioration of one ormore of the above diseases or conditions.

As used herein, “in combination with” or “combination therapies” refersto any form of administration such that additional therapies (e.g.,second, third, fourth, etc.) are still effective in the body (e.g.,multiple compounds are simultaneously effective in the subject, whichmay include synergistic effects of those compounds). Effectiveness maynot correlate to measurable concentration of the agent in blood, serum,or plasma. For example, the different therapeutic compounds can beadministered either in the same formulation or in separate formulations,either concomitantly or sequentially, and on different schedules. Thus,a subject that receives such treatment can benefit from a combinedeffect of different therapies. One or more ActRII-binding proteins ofthe disclosure can be administered concurrently with, prior to, orsubsequent to, one or more other additional agents and/or supportivetherapies. In general, each therapeutic agent will be administered at adose and/or on a time schedule determined for that particular agent. Theparticular combination to employ in a regimen will take into accountcompatibility of the antagonist of the present disclosure with therapyand/or the desired outcome.

The methods and techniques of the present disclosure are generallyperformed according to known conventional methods and as described invarious general and more specific references that are cited anddiscussed throughout the present disclosure unless otherwise indicated.See, e.g., Sambrook et al., Molecular Cloning: A Laboratory Manual, 3rded., Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y.(2001) and Ausubel et al., Current Protocols in Molecular Biology,Greene Publishing Associates (1992), and Harlow and Lane Antibodies: ALaboratory Manual Cold Spring Harbor Laboratory Press, Cold SpringHarbor, N.Y. (1990), all of which are herein incorporated by reference.

The terms “cancer,” “tumor,” “cancerous,” and “malignant” refer to ordescribe the physiological condition in mammals that is typicallycharacterized by unregulated cell growth. Examples of cancers includebut are not limited to, carcinoma including adenocarcinomas, lymphomas,blastomas, melanomas, sarcomas, and leukemias. More particular examplesof such cancers include squamous cell cancer, small-cell lung cancer,non-small cell lung cancer, gastrointestinal cancer, Hodgkin's andnon-Hodgkin's lymphoma, pancreatic cancer, glioblastoma, glioma,cervical cancer, ovarian cancer, liver cancer such as hepatic carcinomaand hepatoma, bladder cancer, breast cancer (including hormonallymediated breast cancer, see, e.g., Innes et al., Br. J. Cancer94:1057-1065 (2006)), colon cancer, colorectal cancer, endometrialcarcinoma, myeloma (such as multiple myeloma), salivary gland carcinoma,basal cell carcinoma, melanoma, prostate cancer, vulval cancer, thyroidcancer, testicular cancer, esophageal cancer, various types of head andneck cancer and cancers of mucinous origins, such as, mucinous ovariancancer, and cholangiocarcinoma (liver). In a particular aspect, thecancer is myelofibrosis, myeloma (e.g., multiple myeloma), or pituitarycancer. In another aspect, the cancer is breast cancer, gastrointestinalcancer, or a carcinoma (e.g., basal and squamous cell carcinomas). In anadditional aspect, the cancer is a bone-loss-inducing cancer.

The terms “polynucleotide” and “nucleic acid” are used interchangeablyand are intended to encompass a singular nucleic acid as well as pluralnucleic acids, and refers to an isolated nucleic acid molecule orconstruct, e.g., messenger RNA (mRNA), complementary DNA (cDNA), orplasmid DNA (pDNA). In certain aspects, a polynucleotide comprises aconventional phosphodiester bond or a non-conventional bond (e.g., anamide bond, such as found in peptide nucleic acids (PNA)). The term“nucleic acid” refers to any one or more nucleic acid segments, e.g.,DNA, cDNA, or RNA fragments, present in a polynucleotide. When appliedto a nucleic acid or polynucleotide, the term “isolated” refers to anucleic acid molecule, DNA or RNA, which has been removed from itsnative environment, for example, a recombinant polynucleotide encodingan antigen binding protein contained in a vector is considered isolatedfor the purposes of the present disclosure. Further examples of anisolated polynucleotide include recombinant polynucleotides maintainedin heterologous host cells or purified (partially or substantially) fromother polynucleotides in a solution. Isolated RNA molecules include invivo or in vitro RNA transcripts of polynucleotides of the presentdisclosure. Isolated polynucleotides or nucleic acids according to thepresent disclosure further include such molecules producedsynthetically. In addition, polynucleotides or nucleic acids can includeregulatory elements such as promoters, enhancers, ribosome bindingsites, or transcription termination signals.

The term “vector” means a construct, which is capable of delivering, andin some aspects expressing, one or more gene(s) or sequence(s) ofinterest in a host cell. Examples of vectors include, but are notlimited to, viral vectors, naked DNA or RNA expression vectors, plasmid,cosmid or phage vectors, DNA or RNA expression vectors associated withcationic condensing agents, DNA or RNA expression vectors encapsulatedin liposomes, and certain eukaryotic cells, such as producer cells.

The term “host cell” refers to a cell or a population of cells harboringor capable of harboring a recombinant nucleic acid. Host cells can beprokaryotic (e.g., E. coli), or eukaryotic. The host cells can be fungalcells including yeast such as Saccharomyces cerevisiae, Pichia pastoris,or Schizosaccharomyces pombe. The host cells also be any of variousanimal cells, such as insect cells (e.g., Sf-9) or mammalian cells(e.g., HEK293F, CHO, COS-7, NIH-3T3, NS0, PER.C6®, and hybridoma). Infurther aspects, the host cells is a CHO cell selected from the groupconsisting of CHO-K, CHO-0 CHO-Lec10, CHO-Lec13, CHO-Lec1, CHO Pro⁻5,and CHO dhfr⁻. In particular aspects, the host cell is a hybridoma.

The terms “polypeptide,” “peptide,” and “protein” are usedinterchangeably herein to refer to polymers of amino acids of anylength. The polymer can be linear or branched, it can comprise modifiedamino acids, and it can be interrupted by non-amino acids. The termsalso encompass an amino acid polymer that has been modified naturally orby intervention; for example, disulfide bond formation, glycosylation,lipidation, acetylation, phosphorylation, or any other manipulation ormodification, such as conjugation with a labeling component. Alsoincluded within the definition are, for example, polypeptides containingone or more analogs of an amino acid (including, for example, unnaturalamino acids, etc.), as well as other modifications known in the art. Itis understood that, because in some aspects the provided ActRII-bindingproteins are based upon antibodies, the ActRII-binding proteins canoccur as single chains or associated chains.

A “recombinant” polypeptide, protein or antibody refers to polypeptide,protein or antibody produced via recombinant DNA technology.Recombinantly produced polypeptides, proteins and antibodies expressedin host cells are considered isolated for the purpose of the presentdisclosure, as are native or recombinant polypeptides which have beenseparated, fractionated, or partially or substantially purified by anysuitable technique.

Also included in the present disclosure are fragments, variants, orderivatives of polypeptides, and any combination thereof. The term“fragment” when referring to polypeptides and proteins include anypolypeptides or proteins which retain at least some of the properties ofthe reference polypeptide or protein. Fragments of polypeptides includeproteolytic fragments, as well as deletion fragments.

The term “variant” refers to an antibody or polypeptide sequence thatdiffers from that of a parent antibody or polypeptide sequence by virtueof at least one amino acid modification. Variants of antibodies orpolypeptides include fragments, and also antibodies or polypeptides withaltered amino acid sequences due to amino acid substitutions, deletions,or insertions. Variants can be naturally or non-naturally occurring.Non-naturally occurring variants can be produced using art-knownmutagenesis techniques. Variant polypeptides can comprise conservativeor non-conservative amino acid substitutions, deletions or additions.

The term “derivatives” as applied to antibodies or polypeptides refersto antibodies or polypeptides which have been altered so as to exhibitadditional features not found on the native antibody or polypeptide. Anexample of a “derivative” antibody is a fusion or a conjugate with asecond polypeptide or another molecule (e.g., a polymer such as PEG, achromophore, or a fluorophore) or atom (e.g., a radioisotope).

The term “amino acid substitution” refers to replacing an amino acidresidue present in a parent sequence with another amino acid residue. Anamino acid can be substituted in a parent sequence, for example, viachemical peptide synthesis or through known recombinant methods.Accordingly, references to a “substitution at position X” or“substitution at position X” refer to the substitution of an amino acidresidue present at position X with an alternative amino acid residue. Insome embodiments, substitution patterns can described according to theschema AXY, wherein A is the single letter code corresponding to theamino acid residue naturally present at position X, and Y is thesubstituting amino acid residue. In other aspects, substitution patternscan described according to the schema XY, wherein Y is the single lettercode corresponding to the amino acid residue substituting the amino acidresidue naturally present at position X.

A “conservative amino acid substitution” is one in which the amino acidresidue is replaced with an amino acid residue having a similar sidechain. Families of amino acid residues having similar side chains havebeen previously defined, including basic side chains (e.g., Lys, Arg,His), acidic side chains (e.g., Asp, Glu), uncharged polar side chains(e.g., Gly, Asp, Gln, Ser, Thr, Tyr, Cys), nonpolar side chains (e.g.,Ala, Val, Leu, Ile, Pro, Phe, Met, Trp), beta-branched side chains(e.g., Thr, Val, Ile) and aromatic side chains (e.g., Tyr, Phe, Trp,His). Thus, if an amino acid residue in a polypeptide is replaced withanother amino acid residue from the same side chain family, thesubstitution is considered to be conservative. In another aspect, astring of amino acid residues can be conservatively replaced with astructurally similar string that differs in order and/or composition ofside chain family members.

Non-conservative substitutions include those in which (a) a residuehaving an electropositive side chain (e.g., Arg, His, or Lys) issubstituted for, or by, an electronegative residue (e.g., Glu or Asp),(b) a hydrophilic residue (e.g., Ser or Thr) is substituted for, or by,a hydrophobic residue (e.g., Ala, Leu, Ile, Phe, or Val), (c) a Cys orPro is substituted for, or by, any other residue, or (d) a residuehaving a bulky hydrophobic or aromatic side chain (e.g., Val, His, Ile,or Trp) is substituted for, or by, one having a smaller side chain(e.g., Ala or Ser) or no side chain (e.g., Gly).

Other substitutions can be readily identified. For example, for theamino acid alanine, a substitution can be taken from any one of D-Ala,Gly, beta-Ala, L-Cys and D-Cys. For lysine, a replacement can be any oneof D-Lys, Arg, D-Arg, homo-Arg, Met, D-Met, omithine, or D-ornithine.Generally, substitutions in functionally important regions that can beexpected to induce changes in the properties of isolated polypeptidesare those in which (a) a polar residue (e.g., Ser or Thr) is substitutedfor (or by) a hydrophobic residue (e.g., Leu, Ile, Phe, or Ala); (b) aCys residue is substituted for (or by) any other residue; (c) a residuehaving an electropositive side chain (e.g., Lys, Arg, or His), issubstituted for (or by) a residue having an electronegative side chain(e.g., Glu or Asp); or (d) a residue having a bulky side chain (e.g.,Phe) is substituted for (or by) one not having such a side chain (e.g.,Gly). The likelihood that one of the foregoing non-conservativesubstitutions can alter functional properties of the protein is alsocorrelated to the position of the substitution with respect tofunctionally important regions of the protein: some non-conservativesubstitutions can accordingly have little or no effect on biologicalproperties.

The term “amino acid insertion” refers to introducing a new amino acidresidue between two amino acid residues present in the parent sequence.An amino acid residue can be inserted in a parent sequence, for example,via chemical peptide synthesis or through recombinant methods known inthe art. Accordingly, the phrases “insertion between positions X and Y”or “insertion between Kabat positions X and Y,” wherein X and Ycorrespond to amino acid residue positions (e.g., a cysteine amino acidresidue insertion between positions 239 and 240), refers to theinsertion of an amino acid residue between the X and Y positions, andalso to the insertion in a nucleic acid sequence of a codon encoding anamino acid residue between the codons encoding the amino acid residuesat positions X and Y.

The term “percent sequence identity” or “percent identity” between twopolynucleotide or polypeptide sequences refers to the number ofidentical matched positions shared by the sequences over a comparisonwindow, taking into account additions or deletions (i.e., gaps) thatmust be introduced for optimal alignment of the two sequences. A matchedposition is any position where an identical nucleotide or amino acid ispresented in both the target and reference sequence. Gaps presented inthe target sequence are not counted since gaps are not nucleotides oramino acids. Likewise, gaps presented in the reference sequence are notcounted since target sequence nucleotides or amino acids are counted,not nucleotides or amino acids from the reference sequence. Thepercentage of sequence identity is calculated by determining the numberof positions at which the identical amino-acid residue or nucleic acidbase occurs in both sequences to yield the number of matched positions,dividing the number of matched positions by the total number ofpositions in the window of comparison and multiplying the result by 100to yield the percentage of sequence identity. The comparison ofsequences and determination of percent sequence identity between twosequences can be accomplished using readily available software programs.Suitable software programs are available from various sources, and foralignment of both protein and nucleotide sequences. One suitable programto determine percent sequence identity is bl2seq, part of the BLASTsuite of program available from the U.S. government's National Centerfor Biotechnology Information BLAST web site (blast.ncbi.nlm.nih.gov).Bl2seq performs a comparison between two sequences using either theBLASTN or BLASTP algorithm. BLASTN is used to compare nucleic acidsequences, while BLASTP is used to compare amino acid sequences. Othersuitable programs are, e.g., Needle, Stretcher, Water, or Matcher, partof the EMBOSS suite of bioinformatics programs and also available fromthe European Bioinformatics Institute (EBI) at www.ebi.ac.uk/Tools/psa.

The structure for carrying a CDR or a set of CDRs will generally be ofan antibody heavy or light chain sequence or substantial portion thereofin which the CDR or set of CDRs is located at a location correspondingto the CDR or set of CDRs of naturally occurring VH and VL antibodyvariable domains encoded by rearranged immunoglobulin genes. Thestructures and locations of immunoglobulin variable domains and theirCDRs can readily be determined by one skilled in the art using programsand known variable domain residue numbering systems such as Chothia,Chothia+, and Kabat can routinely be determined by reference to Kabat(Kabat et al., Sequences of Proteins of Immunological Interest. 4thEdition. U.S. DHHS. 1987, and tools available on the Internet (e.g., atbioinf.org.uk/abysis/sequence_input/key_annotation/key_annotation.html;and immuno.bme.nwu.edu)), herein incorporated by reference in itsentirety.

CDRs can also be carried by other scaffolds such as fibronectin,cytochrome B, albumin (e.g., ALBUdAb (Domantis/GSK) and ALB-Kunitz(Dyax)), unstructured repeat sequences of 3 or 6 amino acids (e.g.,PASylation® technology and XTEN® technology), and sequences containingelastin-like repeat domains (see, e.g., U.S. Pat. Appl. No. 61/442,106,which is herein incorporated by reference in its entirety).

A CDR amino acid sequence substantially as set out herein can be carriedas a CDR in a human variable domain or a substantial portion thereof.The HCDR3 sequences substantially as set out herein representembodiments of the present disclosure and each of these may be carriedas a HCDR3 in a human heavy chain variable domain or a substantialportion thereof.

Variable domains employed in the present disclosure can be obtained fromany germ-line or rearranged human variable domain, or can be a syntheticvariable domain based on consensus sequences of known human variabledomains. A CDR sequence (e.g., CDR3) can be introduced into a repertoireof variable domains lacking a CDR (e.g., CDR3), using recombinant DNAtechnology.

For example, Marks et al., (Bio/Technology 10:779-783 (1992); which isherein incorporated by reference in its entirety) provide methods ofproducing repertoires of antibody variable domains in which consensusprimers directed at or adjacent to the 5′ end of the variable domainarea are used in conjunction with consensus primers to the thirdframework region of human VH genes to provide a repertoire of VHvariable domains lacking a CDR3. Marks et al., further describe how thisrepertoire can be combined with a CDR3 of a particular antibody. Usinganalogous techniques, the CDR3-derived sequences of the presentdisclosure can be shuffled with repertoires of VH or VL domains lackinga CDR3, and the shuffled complete VH or VL domains combined with acognate VL or VH domain to provide antigen binding proteins. Therepertoire can then be displayed in a suitable host system such as thephage display system of Intl. Appl. Publ. No. WO92/01047 or any of asubsequent large body of literature, including Kay et al., (1996) PhageDisplay of Peptides and Proteins: A Laboratory Manual, San Diego:Academic Press, so that suitable antigen binding proteins may beselected. A repertoire can consist of from anything from 104 individualmembers upwards, for example from 10⁶ to 10⁸, or 10¹⁰, members. Othersuitable host systems include yeast display, bacterial display, T7display, and ribosome display. For a review of ribosome display for seeLowe et al., Curr. Pharm. Biotech. 517-527 (2004) and Intl. Appl. Publ.No. WO92/01047, each of which is herein incorporated by reference hereinin its entirety. Analogous shuffling or combinatorial techniques arealso disclosed by Stemmer (Nature 370:389-391 (1994), which is hereinincorporated by reference in its entirety), which describes thetechnique in relation to a β-lactamase gene but observes that theapproach may be used for the generation of antibodies.

An ActRII-binding protein (e.g., an anti-ActRIIA antibody and ananti-ActRIIB antibody) is said to “compete” with a reference moleculefor binding to ActRII (e.g., ActRIIB and/or ActRIIA, respectively) if itbinds to ActRII to the extent that it blocks, to some degree, binding ofthe reference molecule to ActRII. The ability of proteins to compete forbinding to ActRII and thus to interfere with, block or “cross-block” oneanothers binding to ActRII can be determined by any standard competitivebinding assay known in the art including, for example, a competitionELISA assay, surface plasmon resonance (SPR; BIACORE®, Biosensor,Piscataway, N.J.) or according to methods described by Scatchard et al.(Ann. N.Y. Acad. Sci. 51:660-672 (1949)). An ActRII-binding protein maybe said to competitively inhibit binding of the reference molecule toActRII, for example, by at least 90%, at least 80%, at least 70%, atleast 60%, or at least 50%. According to some aspects, theActRII-binding protein competitively inhibits binding of the referencemolecule to ActRIIA, by at least 90%, at least 80%, at least 70%, atleast 60%, or at least 50%. According to other aspects, theActRII-binding protein competitively inhibits binding of a referencemolecule to ActRIIB, by at least 90%, at least 80%, at least 70%, atleast 60%, or at least 50%.

ActRII-Binding Proteins

Proteins that specifically bind ActRII are provided.

In some aspects, the ActRII-binding protein binds ActRII with anaffinity that is at least, 100, 500, or 1000 times greater than theaffinity of the ActRII-binding protein for a control protein that is nota TGF-beta receptor family member. In certain aspects, theActRII-binding protein binds ActRII and has a dissociation constant(K_(D)) of <1 μM, <100 nM, <10 nM, <1 nM, <0.1 nM, <10 pM, <1 pM, or<0.1 pM. In some aspects, the ActRII-binding protein has a K_(D) forhuman ActRII within the range of ≤1 μM and ≥0.1 pM, ≤100 μM and ≥0.1 pM,or ≤100 μM and ≥1 pM.

In some aspects, BIACORE® analysis is used to determine the ability ofan ActRII-binding protein (e.g., an anti-ActRII antibody) to competewith/block the binding to ActRII protein by a reference ActRII-bindingprotein (e.g., an anti-ActRII antibody). In a further aspect in which aBIACORE® instrument (for example the BIACORE® 3000) is operatedaccording to the manufacturer's recommendations, ActRII-Fc fusionprotein is captured on a CM5 BIACORE® chip by previously attachedanti-niFc IgG to generate an ActRII-coated surface. Typically 200-800resonance units of ActRII-Fc (dimeric) would be coupled to the chip (anamount that gives easily measurable levels of binding but that isreadily saturable by the concentrations of test reagent being used).

The two ActRII-binding proteins (termed A* and B*) to be assessed fortheir ability to compete with/block each other are mixed at a one to onemolar ratio of binding sites in a suitable buffer to create a testmixture. When calculating the concentrations on a binding site basis themolecular weight of an ActRII-binding protein is assumed to be the totalmolecular weight of the ActRII-binding protein divided by the number ofActRII-binding sites on that ActRII-binding protein. The concentrationof each ActRII-binding protein (i.e., A* and B*) in the test mixtureshould be high enough to readily saturate the binding sites for thatActRII-binding protein on the ActRII-Fc molecules captured on theBIACORE® chip. The A* and B* ActRII-binding proteins in the mixture areat the same molar concentration (on a binding basis) and thatconcentration would typically be between 1.00 and 1.5 micromolar (on abinding site basis). Separate solutions containing ActRII-bindingprotein A* alone and ActRII-binding protein B* alone are also prepared.ActRII-binding protein A* and ActRII-binding protein B* in thesesolutions should be in the same buffer and at the same concentration asin the test mixture. The test mixture is passed over theActRII-Fc-coated BIACORE® chip and the total amount of binding recorded.The chip is then treated in such a way as to remove the boundActRII-binding proteins without damaging the chip-bound ActRII-Fc.Typically, this is done by treating the chip with 30 mM HCl for 60seconds. The solution of ActRII-binding protein A* alone is then passedover the ActRII-Fc-coated surface and the amount of binding recorded.The chip is again treated to remove the bound antibody without damagingthe chip-bound ActRII-Fc. The solution of ActRII-binding protein B*alone is then passed over the ActRII-Fc-coated surface and the amount ofbinding recorded. The maximum theoretical binding of the mixture ofActRII-binding protein A* and ActRII-binding protein B* is nextcalculated, and is the sum of the binding of each ActRII-binding proteinwhen passed over the ActRII surface alone. If the actual recordedbinding of the mixture is less than this theoretical maximum then thetwo ActRII-binding proteins are competing with/blocking each other.Thus, in general, a blocking ActRII-binding protein is one which willbind to ActRII in the above BIACORE® blocking assay such that during theassay and in the presence of a second ActRII-binding protein therecorded binding is between 80% and 0.1% (e.g., 80%> to 4%) of themaximum theoretical binding, specifically between 75% and 0.1% (e.g.,75% to 4%) of the maximum theoretical binding, and more specificallybetween 70% and 0.1% (e.g., 70% to 4%) of maximum theoretical binding(as defined above) of the two ActRII-binding proteins in combination.

The BIACORE® assay described above is an exemplary assay used todetermine if two ActRII-binding proteins such as anti-ActRII antibodiescompete with/block each other for binding ActRII. On rare occasions,particular ActRII-binding proteins may not bind to ActRII-Fc coupled viaanti-Fc IgG to a CM5 BIACORE® chip (this might occur when the relevantbinding site on ActRII is masked or destroyed by ActRII linkage to Fc).In such cases, blocking can be determined using a tagged version ofActRII, for example C-terminal His-tagged ActRII. In this particularformat, an anti-His antibody would be coupled to the BIACORE® chip andthen the His-tagged ActRII would be passed over the surface of the chipand captured by the anti-His antibody. The cross-blocking analysis wouldbe carried out essentially as described above, except that after eachchip regeneration cycle, new His-tagged ActRII would be loaded back ontothe surface coated with anti-His antibody. Moreover, various other knowntags and tag binding protein combinations can be used for such ablocking analysis (e.g., HA tag with anti-HA antibodies; FLAG tag withanti-FLAG antibodies; biotin tag with streptavidin). The followinggenerally describes an ELISA assay for determining whether anActRII-binding protein blocks or is capable of blocking the binding of areference ActRII-binding protein to ActRII.

In some aspects, an ELISA is used to determine the ability of anActRII-binding protein (e.g., an anti-ActRII antibody) to compete forbinding to the ActRII protein with a reference ActRII-binding protein(e.g., an anti-ActRII antibody or ActRII ligand). The general principleof such an assay is to have a reference ActRII-binding protein (e.g., ananti-ActRII antibody) coated onto the wells of an ELISA plate. An excessamount of a second potentially blocking, test ActRII-binding protein isadded in solution (i.e., not bound to the ELISA plate). A limited amountof ActRII (or alternatively ActRII-Fc) is then added to the wells. Thecoated reference ActRII-binding protein and the test ActRII-bindingprotein in solution compete for binding of the limited number of ActRII(or ActRII-Fc) molecules. The plate is washed to remove ActRII that hasnot been bound by the coated reference ActRII-binding protein and toalso remove the test, solution-phase ActRII-binding protein as well asany complexes formed between the test, solution-phase ActRII-bindingprotein and ActRII. The amount of bound ActRII is then measured using anappropriate ActRII detection reagent. A test ActRII-binding protein insolution that is able to block binding of the coated referenceActRII-binding protein to ActRII will be able to cause a decrease in thenumber of ActRII molecules that the coated reference ActRII-bindingprotein can bind relative to the number of ActRII molecules that thecoated reference ActRII-binding protein can bind in the absence of thesecond, solution-phase test ActRII-binding protein. The backgroundsignal for the assay is defined as the signal obtained in wells with thecoated reference ActRII-binding protein, solution-phase testActRII-binding protein, ActRII buffer only (i.e., no ActRII) and ActRIIdetection reagents. The positive control signal for the assay is definedas the signal obtained in wells with the coated reference ActRII-bindingprotein, solution-phase test ActRII-binding protein buffer only (i.e.,no solution-phase test ActRII-binding protein), ActRII and ActRIIdetection reagents. The ELISA assay is be run in such a manner so as tohave the positive control signal at least 3 times the background signal.As a control for methodologic artifacts, the cross-blocking assay may berun in the format just described and also reversed, with the testActRII-binding protein as the coated antibody and the referenceActRII-binding protein as the solution-phase antibody.

In some aspects, a reporter gene assay is used to determine the abilityof an ActRII-binding protein (e.g., an anti-ActRII antibody) toneutralize ActRII (e.g., ActRIIB). In some aspects, the reporter geneassay is performed using recombinant A204 cells to determine the abilityof an ActRII-binding protein (e.g., an anti-ActRII antibody) toneutralize ActRII (e.g., ActRIIB) activity. This assay is based on ahuman rhabdomyosarcoma cell line transfected with a pGL3(CAGA)12 plasmidcontaining a (CAGA)12 motif (see, e.g., Dennler et al., EMBO17:3091-3100 (1998) and U.S. Pat. No. 8,765,385, each of which in hereinincorporated by reference in its entirety) as well as a ReniUa reporterplasmid (pRLCMV) to control for transfection efficiency. The CAGA12motif is present in TGF-beta responsive genes (PAI-1 gene), so thisvector is of general use for factors signaling through Smad2 and Smad3.With respect to measuring the ActRIIB-binding activity of a candidateprotein using this assay, since the A204 cell line expresses primarilyActRIIA rather than ActRIIB, it is not possible to directly testantibodies for potential ActRIIB neutralizing ability. Instead, thisassay is designed to detect the ability of a test ActRII protein bindingcandidate to neutralize the inhibitory effect of the soluble fusionprotein ActRIIB-Fc on activation of endogenous ActRIIA by ligands (suchas activin A or GDF11) that can bind with high affinity to both ActRIIBand ActRIIA. Thus, in this assay, ligand-mediated activation of ActRIIAwill occur despite the presence of ActRIIB-Fc if the ActRIIB-binding isneutralizing.

On the first day of the assay, A204 cells (ATCC HTB-82) are distributedin 48-well plates at 10⁵ cells per well. On the second day, a solutioncontaining 10 μg pGL3(CAGA)12, 1 μg pRLCMV, 30 μl Fugene 6 (RocheDiagnostics), and 970 μl OptiMEM (Invitrogen) is preincubated for 30minutes, then added to McCoy's growth medium, which is applied to theplated cells (500 μl/well) for incubation overnight at room temperature.On the third day, medium is removed, and cells are incubated for 6 hoursat 37° C. with a mixture of ligands and inhibitors prepared as describedbelow.

According to one aspect, the neutralizing potency of an ActRII-bindingprotein such as an anti-ActRII antibody, is evaluated whereby a serialdilution of the test protein is made in a 48-well plate in a 200 μlvolume of assay buffer (McCoy's medium+0.1% BSA). For assays assessingthe ability of a candidate protein to neutralize ActRIIB activity, anequal volume of ActRIIB-Fc (200 μg/ml) in assay buffer is then added.The test solutions are incubated at 37° C. for 30 minutes, then 400 μlof activin A (10 ng/ml) is added to all wells, and 350 μl of thismixture is added to each well of the 48-well plate of A204 cells. Eachconcentration of test protein is tested in duplicate. For assaysassessing the ability of a candidate protein to neutralize ActRIIBactivity, the final concentration of ActRIIB-Fc is 50 ng/ml (which isthe IC₅₀ for this inhibitor of activin A signaling when the finalconcentration of activin A is 5 ng/ml). After incubation with testsolutions for 6 hours, cells are rinsed with phosphate-buffered salinecontaining 0.1% BSA, then lysed with passive lysis buffer (PromegaE1941) and stored overnight at −70° C. On the fourth and final day,plates are warmed to room temperature with gentle shaking. Cell lysatesare transferred in duplicate to a chemoluminescence plate (96-well) andanalyzed in a luminometer with reagents from a Dual-Luciferase ReporterAssay system (Promega E1980) to determine normalized luciferaseactivity.

Pharmacodynamic parameters dependent on ActRIIB signaling can bemeasured as endpoints for in vivo testing of ActRIIB-binding proteins inorder to identify those binding proteins that are able to neutralizeActRIIB and provide a therapeutic benefit. An ActRIIB neutralizingbinding agent is defined as one capable of causing a statisticallysignificant change, as compared to vehicle-treated animals, in such apharmacodynamic parameter. Such in vivo testing can be performed in anysuitable mammal (e.g., mouse, rat, or monkey).

In some aspects, the ActRII-binding protein binds ActRIIA with anaffinity that is at least, 100, 500, or 1000 times greater than theaffinity of the ActRII-binding protein for a control protein that is nota TGF-beta receptor family member. In additional aspects, theActRII-binding protein binds ActRIIA with an affinity that is at least,100, 500, or 1000 times greater than the affinity of the ActRII-bindingprotein for a control protein that is not a TGF-beta receptor familymember. In certain aspects, the ActRIIA-binding protein binds ActRIIAand has a dissociation constant (K_(D)) of <1 μM, <100 nM, <10 nM, <1nM, <0.1 nM, <10 pM, <1 pM, or <0.1 pM. In some aspects, theActRIIA-binding protein has a K_(D) for human ActRIIA within the rangeof ≤1 μM and ≥0.1 pM, ≤100 μM and ≥0.1 pM, or ≤100 μM and ≥1 pM.

In some aspects, the ActRII-binding protein binds ActRIIB with anaffinity that is at least, 100, 500, or 1000 times greater than theaffinity of the ActRII-binding protein for a control protein that is nota TGF-beta family member. In additional aspects, the ActRII-bindingprotein binds ActRIIB with an affinity that is at least, 100, 500, or1000 times greater than the affinity of the ActRII-binding protein for acontrol protein that is not a TGF-beta receptor family member. Incertain aspects, the ActRIIB-binding protein binds ActRIIB and has adissociation constant (K_(D)) of <1 μM, <100 nM, <10 nM, <1 nM, <0.1 nM,<10 pM, <1 pM, or <0.1 pM. In some aspects, the ActRIIB-binding proteinhas a K_(D) for human ActRIIB within the range of ≤1 μM and ≥0.1 pM,≤100 μM and ≥0.1 pM, or ≤100 μM and ≥1 pM.

In some aspects, the ActRII-binding protein binds ActRIIB and ActRIIAwith an affinity that is at least, 100, 500, or 1000 times greater thanthe affinity of the ActRII-binding protein for a control protein that isnot a TGF-beta family member. In additional aspects, the ActRII-bindingprotein binds ActRIIB and ActRIIA with an affinity that is at least,100, 500, or 1000 times greater than the affinity of the ActRII-bindingprotein for a control protein that is not a TGF-beta receptor familymember. In certain aspects, the ActRII-binding protein binds ActRIIB andActRIIA and has a dissociation constant (K_(D)) of <1 μM, <100 nM, <10nM, <1 nM, <0.1 nM, <10 pM, <1 pM, or <0.1 pM. In some aspects, theActRIIA- and ActRIIB-binding protein has a K_(D) for human ActRIIB andActRIIA within the range of ≤1 μM and ≥0.1 pM, ≤100 μM and ≥0.1 pM, or≤100 μM and ≥1 pM.

In some aspects, an ActRII-binding protein is an antibody thatspecifically binds ActRII. In additional aspects, the ActRII-bindingprotein is a full-length anti-ActRIIA antibody or a full-lengthanti-ActRIIB antibody. In additional aspects, the antibody is amonoclonal antibody, a recombinant antibody, a human antibody, ahumanized antibody, a chimeric antibody, a bi-specific antibody, amulti-specific antibody, or an ActRII-binding antibody fragment thereof.In additional aspects, the antibody specifically binds ActRIIB and/orActRIIA.

In some aspects, the ActRII-binding protein (e.g., an anti-ActRIIantibody and an ActRII-binding antibody fragment) can bind to ActRIImolecules across species.

The mature ActRIIA extracellular domain of human ActRIIA (SEQ ID NO:138)differs from that of the mouse ActRIIA ortholog (Ref. P27038) by onlytwo conserved amino acid substitutions (i.e., K19R and V72I). Inadditional aspects, the ActRII-binding protein can bind to human ActRIIA(hActRIIA) and murine ActRIIA (murActRIIA). In certain aspects, theActRII-binding protein is an anti-ActRIIA antibody (e.g., a full-lengthActRIIA-antibody and an ActRIIA-binding antibody fragment, and a variantand derivative thereof) can specifically bind to ActRIIA (e.g., hActRIIAor murActRIIA) with a dissociation constant or K_(D) of less than 10⁻⁸M, than less than 10⁻⁹ M, or less than 10⁻¹⁰ M, as determined byBIACORE® or KINEXA®. In further aspects, the anti-ActRIIA antibody bindsto ActRIIA with a K_(D) of <1 nM (e.g., as determined by BIACORE®analysis). In a further aspect, the anti-ActRIIA antibody binds toActRIIA with a K_(D) within one order of magnitude of 1 nM or within twoorders of magnitude of 1 nM. In some aspects, the ActRIIA-bindingprotein has a K_(D) for human ActRIIA within the range of ≤1 μM and ≥0.1pM, ≤100 μM and ≥0.1 pM, or ≤100 μM and ≥1 pM.

The mature extracellular domain of human ActRIIB (SEQ ID NO:139) differsfrom the corresponding sequence of the mouse ActRIIB ortholog (NCBI Ref.Seq. NP 031423) by one amino acid substitution (i.e., A95P). In certainaspects, the ActRII-binding protein is an anti-ActRIIB antibody (e.g., afull-length ActRIIB-antibody and an ActRIIB-binding antibody fragment,and a variant and derivative thereof) that specifically binds ActRIIB(e.g., hActRIIB and murActRIIB) with a dissociation constant or K_(D) ofless than 10⁻⁸ M, less than 10⁻⁹ M, or less than 10⁻¹⁰ M as determinedby BIACORE® or KINEXA®. In further aspects, the anti-ActRIIB antibodybinds to ActRIIB with a K_(D) of <1 nM as determined by BIACORE® orKINEXA® analysis. In a further aspect, the anti-ActRIIB antibody bindsActRIIB with a K_(D) within one order of magnitude of 1 nM or within twoorders of magnitude of 1 nM. In some aspects, the ActRIIB-bindingprotein has a K_(D) for human ActRIIB within the range of ≤1 μM and ≥0.1pM, ≤100 μM and ≥0.1 pM, or ≤1 nM and ≥1 pM.

In some aspects, anti-ActRII antibody is an ActRII-binding antibodyfragment. In some aspects, the ActRII-binding antibody fragment is a:Fab, Fab′, F(ab′)₂, Fv fragment, diabody, or single chain antibodymolecule. In additional aspects, the ActRII-antibody is a Fd, singlechain Fv(scFv), disulfide linked Fv, V-NAR domain, IgNar, intrabody,IgGACH2, minibody, F(ab′)₃ tetrabody, triabody, diabody, single-domainantibody, DVD-Ig, Fcab, mAb², (scFv)₂, scFv-Fc or bis-scFv.

In additional aspects the ActRII-binding protein is an antibody thatincludes a VH and a VL. In some aspects the anti-ActRII antibody furtherincludes a heavy chain constant region or fragment thereof. In someaspects, the antibody comprises a heavy chain immunoglobulin constantregion selected from the group consisting of: (a) a human IgA constantregion, or fragment thereof; (b) a human IgD constant region, orfragment thereof; (c) a human IgE constant domain, or fragment thereof;(d) a human IgG1 constant region, or fragment thereof; (e) a human IgG2constant region, or fragment thereof; (f) a human IgG3 constant region,or fragment thereof; (g) a human IgG4 constant region, or fragmentthereof; and (h) a human IgM constant region, or fragment thereof. Incertain aspects an ActRII-binding protein comprises a heavy chainconstant region or fragment thereof, e.g., a human IgG constant regionor fragment thereof. In further aspects, the ActRII-binding proteincomprises a heavy chain immunoglobulin constant domain that has, or hasbeen mutated to have altered effector function and/or half-life.

In particular aspects, the ActRII-binding protein is an antibody thatcomprises an IgG1 heavy chain constant region containing a mutation thatdecreases effector function (see, e.g., Idusogie et al., J. Immunol.166:2571-2575 (2001); Sazinsky et al., PNAS USA 105:20167-20172 (2008);Davis et al., J. Rheumatol. 34:2204-2210 (2007); Bolt et al., Eur. J.Immunol. 23:403-411 (1993); Alegre et al., Transplantation 57:1537-1543(1994); Xu et al., Cell Immunol. 200:16-26 (2000); Cole et al.,Transplantation 68:563-571 (1999); Hutchins et al., PNAS USA92:11980-11984 (1995); Reddy et al., J. Immunol. 164:1925-1933 (2000);WO97/11971, and WO07/106585; U.S. Appl. Publ. 2007/0148167A1; McEarchernet al., Blood 109:1185-1192 (2007); Strohl, Curr. Op. Biotechnol.20:685-691 (2009); and Kumagai et al., J. Clin. Pharmacol. 47:1489-1497(2007), each of which is herein incorporated by reference in itsentirety).

In some aspects, the heavy chain constant region or fragment thereofincludes one or more amino acid substitutions relative to a wild-typeIgG constant domain wherein the modified IgG has decreased ADCC comparedto the half-life of an IgG having the wild-type IgG constant domain.Examples of Fc sequence engineering modifications contained in theprovided antibodies that decrease ADCC include one or more modificationscorresponding to: IgG1-K326W, E333S; IgG2-E333S; IgG1-N297A; IgG1-L234A,L235A; IgG2-V234A, G237A; IgG4-L235A, G237A, E318A; IgG4-S228P, L236E;IgG2-EU sequence 118-260; IgG4-EU sequence 261-447; IgG2-H268Q, V309L,A330S, A331S; IgG1-C220S, C226S, C229S, P238S; IgG1-C226S, C229S, E233P,L234V, L235A; and IgG1-L234F, L235E, P331S, wherein the positionnumbering is according to the EU index as in Kabat.

In certain aspects an ActRII-binding protein comprises a heavy chainimmunoglobulin constant domain that has, or has been mutated to have,reduced CDC activity. In particular aspects, the ActRII-binding proteinis an antibody that comprises an IgG1 heavy chain constant regioncontaining a mutation that decreases CDC activity (see, e.g., WO97/11971and WO07/106585; U.S. Appl. Publ. 2007/0148167A1; McEarchern et al.,Blood 109:1185-1192 (2007); Hayden-Ledbetter et al., Clin. Cancer15:2739-2746 (2009); Lazar et al., PNAS USA 103:4005-4010 (2006);Bruckheimer et al., Neoplasia 11:509-517 (2009); Strohl, Curr. Op.Biotechnol. 20:685-691 (2009); and Sazinsky et al., PNAS USA105:20167-20172 (2008); each of which is herein incorporated byreference in its entirety). Examples of Fc sequence engineeringmodifications contained in an anti-ActRII antibody that decrease CDCinclude one or more modifications corresponding to: IgG1-S239D, A330L,I332E; IgG2 EU sequence 118-260; IgG4-EU sequence 261-447; IgG2-H268Q,V309L, A330S, A331S; IgG1-C226S, C229S, E233P, L234V, L235A; IgG1-L234F,L235E, P331S; and IgG1-C226S, P230S.

In further aspects, the heavy chain constant region or fragment thereofincludes one or more amino acid substitutions relative to a wild-typeIgG constant domain wherein the modified IgG has an increased half-lifecompared to the half-life of an IgG having the wild-type IgG constantdomain. For example, the IgG constant domain can contain one or moreamino acid substitutions of amino acid residues at positions 251-257,285-290, 308-314, 385-389, and 428-436, wherein the amino acid positionnumbering is according to the EU index as set forth in Kabat. In certainaspects the IgG constant domain can contain one or more of asubstitution of the amino acid at Kabat position 252 with Tyr, Phe, Trp,or Thr; a substitution of the amino acid at Kabat position 254 with Thr;a substitution of the amino acid at Kabat position 256 with Ser, Arg,Gln, Glu, Asp, or Thr; a substitution of the amino acid at Kabatposition 257 with Leu; a substitution of the amino acid at Kabatposition 309 with Pro; a substitution of the amino acid at Kabatposition 311 with Ser; a substitution of the amino acid at Kabatposition 428 with Thr, Leu, Phe, or Ser; a substitution of the aminoacid at Kabat position 433 with Arg, Ser, Iso, Pro, or Gln; or asubstitution of the amino acid at Kabat position 434 with Trp, Met, Ser,His, Phe, or Tyr. More specifically, the IgG constant domain can containamino acid substitutions relative to a wild-type human IgG constantdomain including a substitution of the amino acid at Kabat position 252with Tyr, a substitution of the amino acid at Kabat position 254 withThr, and a substitution of the amino acid at Kabat position 256 withGlu.

In additional aspects, the ActRII-binding protein is an antibody thatcomprises a light chain immunoglobulin constant region. In a furtheraspect, the antibody comprises a human Ig kappa constant region or ahuman Ig lambda constant region.

In some aspects, the ActRII-binding protein comprises a set of CDRs:VH-CDR1, VH-CDR2, VH-CDR3, VL-CDR1, VL-CDR2 and VL-CDR3, wherein theCDRs are present in a VH and a VL pair disclosed in Table 1. In furtherembodiments, the ActRII-binding protein comprises a set of CDRs whereinthe CDRs are present in a VH and a VL pair selected from the groupconsisting of: (a) a VH sequence of SEQ ID NO:2, 16, 22, 28, 34, or 40,and a VL sequence of SEQ ID NO:9, and wherein the protein binds ActRIIB,(b) a VH sequence of SEQ ID NO:63 or 77, and a VL having the amino acidsequence of SEQ ID NO:70, and wherein the protein binds ActRIIB; (c) aVH sequence of SEQ ID NO:45 or 57, and a VL sequence of SEQ ID NO:50,and wherein the protein binds ActRIIB; (d) a VH sequence of SEQ IDNO:84, 98, 105, 112, or 119, and a VL sequence of SEQ ID NO:91, andwherein the protein binds ActRIIA, and (e) a VH sequence of SEQ IDNO:125, and a VL sequence of SEQ ID NO:132, and wherein the proteinbinds ActRIIA.

In further embodiments, the ActRII-binding protein comprises a set ofCDRs wherein the CDRs are present in a VH and a VL pair having: (a) a VHsequence of SEQ ID NO:144, and a VL sequence of SEQ ID NO:151, andwherein the protein binds ActRIIB.

In further embodiments, the ActRII-binding protein comprises a set ofCDRs wherein the CDRs are present in a VH and a VL pair having: (a) a VHsequence of SEQ ID NO:165, and a VL sequence of SEQ ID NO:172, andwherein the protein binds ActIIRA and ActRIIB.

In some aspects an ActRII-binding protein comprises a set of CDRs: (a)VH-CDR1, VH-CDR2, and VH-CDR3, or (b) VL-CDR1, VL-CDR2, and VL-CDR3,wherein the set of CDRs is identical to, or has a total of one, two,three, four, five, six, seven, eight, nine, ten, or fewer than ten,amino acid substitutions, deletions, and/or insertions from a referenceset of CDRs disclosed herein. In further aspects, the ActRII-bindingprotein comprises a set of CDRs, wherein the set of CDRs is identicalto, or has a total of one, two, three, four, five, six, seven, eight,nine, ten, or fewer than ten, amino acid substitutions, deletions,and/or insertions from a reference set of CDRs in a VH or VL sequencedisclosed in Table 1.

In some aspects an ActRII-binding protein comprises a set of CDRs:VH-CDR1, VH-CDR2, VH-CDR3, VL-CDR1, VL-CDR2, and VL-CDR3, wherein theset of CDRs is identical to, or has a total of one, two, three, four,five, six, seven, eight, nine, ten, or fewer than ten, amino acidsubstitutions, deletions, and/or insertions from a reference set of CDRsdisclosed herein. In further aspects, the ActRII-binding proteincomprises a set of CDRs, wherein the set of CDRs is identical to, or hasa total of one, two, three, four, five, six, seven, eight, nine, ten, orfewer than ten, amino acid substitutions, deletions, and/or insertionsfrom a reference set of CDRs in a VH and VL sequence pair disclosed inTable 1.

In additional aspects, the ActRII-binding protein specifically bindsActRII and comprises a set of CDRs: VH-CDR1, VH-CDR2, VH-CDR3, VL-CDR1,VL-CDR2, and VL-CDR3, wherein the set of CDRs is identical to, or has atotal of one, two, three, four, five, six, seven, eight, nine, ten, orfewer than ten, amino acid substitutions, deletions, and/or insertionsfrom a reference set of CDRs in which: (a)(i) VH-CDR1 has the amino acidsequence of SEQ ID NO:3, 17, 23, 29, 35 or 41; (ii) VH-CDR2 has theamino acid sequence of SEQ ID NO:4, 18, 24, 30, 178, or 36; (iii)VH-CDR3 has the amino acid sequence of SEQ ID NO:5; (iv) VL-CDR1 has theamino acid sequence of SEQ ID NO:10; (v) VL-CDR2 has the amino acidsequence of SEQ ID NO:11; and (vi) VL-CDR3 has the amino acid sequenceof SEQ ID NO:12; and wherein the protein binds ActRIIB; (b)(i) VH-CDR1has the amino acid sequence of SEQ ID NO:64 or 78; (ii) VH-CDR2 has theamino acid sequence of SEQ ID NO:65 or 79; (iii) VH-CDR3 has the aminoacid sequence of SEQ ID NO:66 or 80; (iv) VL-CDR1 has the amino acidsequence of SEQ ID NO:71; (v) VL-CDR2 has the amino acid sequence of SEQID NO:72; and (vi) VL-CDR3 has the amino acid sequence of SEQ ID NO:73;and wherein the protein binds ActRIIB; (c)(i) VH-CDR1 has the amino acidsequence of SEQ ID NO:3 or 58; (ii) VH-CDR2 has the amino acid sequenceof SEQ ID NO:4 or 59; (iii) VH-CDR3 has the amino acid sequence of SEQID NO:46; (iv) VL-CDR1 has the amino acid sequence of SEQ ID NO:51; (v)VL-CDR2 has the amino acid sequence of SEQ ID NO:52; and (vi) VL-CDR3has the amino acid sequence of SEQ ID NO:53; and wherein the proteinbinds ActRIIB; (d)(i) VH-CDR1 has the amino acid sequence of SEQ IDNO:85, 99, 106, 166, or 113; (ii) VH-CDR2 has the amino acid sequence ofSEQ ID NO:86, 100, 107, 114, 167, or 120; (iii) VH-CDR3 has the aminoacid sequence of SEQ ID NO:87, 101, 108, 115, 168, or 121; (iv) VL-CDR1has the amino acid sequence of SEQ ID NO:92, or 173; (v) VL-CDR2 has theamino acid sequence of SEQ ID NO:93, 153, or 174; and (vi) VL-CDR3 hasthe amino acid sequence of SEQ ID NO:94, or 175; and wherein the proteinbinds ActRIIB and ActRIIA; or (e)(i) VH-CDR1 has the amino acid sequenceof SEQ ID NO:126; (ii) VH-CDR2 has the amino acid sequence of SEQ IDNO:127; (iii) VH-CDR3 has the amino acid sequence of SEQ ID NO:128; (iv)VL-CDR1 has the amino acid sequence of SEQ ID NO:133; (v) VL-CDR2 hasthe amino acid sequence of SEQ ID NO:134; and (vi) VL-CDR3 has the aminoacid sequence of SEQ ID NO:135; and wherein the protein binds ActRIIA.In further aspects, the ActRIIB-binding protein has at least onecharacteristic selected from the group consisting of: (a) competes withan ActRII ligand (e.g., activin A, activin B, GDF1, GDF3, GDF8(myostatin), GDF11, BMP6, BMP7, BMP9, or BMP10) for binding to ActRII;(b) decreases the phosphorylation of Smads (e.g., Smad2 and/or Smad3) incells expressing ActRII in the presence of an ActRII ligand (e.g.,activin A or GDF8); (c) decreases the phosphorylation of ALK4 and/orALK7 in cells expressing ActRII and ALK4 and/or ALK7 in the presence ofan ActRII ligand; and (d) binds to ActRII with a K_(D) of ≤1 nM and ≥1pM (e.g., as determined by BIACORE® analysis). In some aspects, theActRII-binding protein has 2, 3, or 4 of the above characteristics. Insome aspects, the ActRII-binding protein has at least 2 or at least 3 ofthe above characteristics.

In additional aspects, the ActRII-binding protein specifically bindsActRII and comprises a set of CDRs: VH-CDR1, VH-CDR2, VH-CDR3, VL-CDR1,VL-CDR2, and VL-CDR3, wherein the set of CDRs is identical to, or has atotal of one, two, three, four, five, six, seven, eight, nine, ten, orfewer than ten, amino acid substitutions, deletions, and/or insertionsfrom a reference set of CDRs in which (i) VH-CDR1 has the amino acidsequence of SEQ ID NO:145; (ii) VH-CDR2 has the amino acid sequence ofSEQ ID NO:146; (iii) VH-CDR3 has the amino acid sequence of SEQ IDNO:147; (iv) VL-CDR1 has the amino acid sequence of SEQ ID NO:152; (v)VL-CDR2 has the amino acid sequence of SEQ ID NO:153; and (vi) VL-CDR3has the amino acid sequence of SEQ ID NO:154; and wherein the proteinbinds ActRIIB. In further aspects, the ActRIIB-binding protein has atleast one characteristic selected from the group consisting of: (a)competes with an ActRII ligand (e.g., activin A, activin B, GDF1, GDF3,GDF8 (myostatin), GDF11, BMP6, BMP7, BMP9, or BMP10) for binding toActRII; (b) decreases the phosphorylation of Smads (e.g., Smad2 and/orSmad3) in cells expressing ActRII in the presence of an ActRII ligand(e.g., activin A or GDF8); (c) decreases the phosphorylation of ALK4and/or ALK7 in cells expressing ActRII and ALK4 and/or ALK7 in thepresence of an ActRII ligand; and (d) binds to ActRII with a K_(D) of ≤1nM and ≥1 pM (e.g., as determined by BIACORE® analysis). In someaspects, the ActRII-binding protein has 2, 3, or 4 of the abovecharacteristics. In some aspects, the ActRII-binding protein has atleast 2 or at least 3 of the above characteristics.

In additional aspects, the ActRII-binding protein specifically bindsActRII and comprises a set of CDRs: VH-CDR1, VH-CDR2, VH-CDR3, VL-CDR1,VL-CDR2, and VL-CDR3, wherein the set of CDRs is identical to, or has atotal of one, two, three, four, five, six, seven, eight, nine, ten, orfewer than ten, amino acid substitutions, deletions, and/or insertionsfrom a reference set of CDRs in which (i) VH-CDR1 has the amino acidsequence of SEQ ID NO:166; (ii) VH-CDR2 has the amino acid sequence ofSEQ ID NO:167; (iii) VH-CDR3 has the amino acid sequence of SEQ IDNO:168; (iv) VL-CDR1 has the amino acid sequence of SEQ ID NO:173; (v)VL-CDR2 has the amino acid sequence of SEQ ID NO:174; and (vi) VL-CDR3has the amino acid sequence of SEQ ID NO:175; and wherein the proteinbinds ActIIRA and ActRIIB. In further aspects, the ActRII-bindingprotein has at least one characteristic selected from the groupconsisting of: (a) competes with an ActRII ligand (e.g., activin A,activin B, GDF1, GDF3, GDF8 (myostatin), GDF11, BMP6, BMP7, BMP9, orBMP10) for binding to ActRII; (b) decreases the phosphorylation of Smads(e.g., Smad2 and/or Smad3) in cells expressing ActRII in the presence ofan ActRII ligand (e.g., activin A or GDF8); (c) decreases thephosphorylation of ALK4 and/or ALK7 in cells expressing ActRII and ALK4and/or ALK7 in the presence of an ActRII ligand; and (d) binds to ActRIIwith a K_(D) of ≤1 nM and ≥1 pM (e.g., as determined by BIACORE®analysis). In some aspects, the ActRII-binding protein has 2, 3, or 4 ofthe above characteristics. In some aspects, the ActRII-binding proteinhas at least 2 or at least 3 of the above characteristics.

In some aspects, the ActRII-binding protein specifically binds ActRIIand comprises a set of CDRs that has a total of one, two, three, four,five, six, seven, eight, nine, ten, fewer than ten, or zero, amino acidsubstitutions, deletions, and/or insertions from a reference set of CDRsin which: (a)(i) VH-CDR1 has the amino acid sequence of SEQ ID NO:3;(ii) VH-CDR2 has the amino acid sequence of SEQ ID NO:4; (iii) VH-CDR3has the amino acid sequence of SEQ ID NO:5; (iv) VL-CDR1 has the aminoacid sequence of SEQ ID NO:10; (v) VL-CDR2 has the amino acid sequenceof SEQ ID NO:11; and (vi) VL-CDR3 has the amino acid sequence of SEQ IDNO:12; and wherein the protein binds ActRIIB; (b)(i) VH-CDR1 has theamino acid sequence of SEQ ID NO:17; (ii) VH-CDR2 has the amino acidsequence of SEQ ID NO:18; (iii) VH-CDR3 has the amino acid sequence ofSEQ ID NO:5; (iv) VL-CDR1 has the amino acid sequence of SEQ ID NO:10;(v) VL-CDR2 has the amino acid sequence of SEQ ID NO:11; and (vi)VL-CDR3 has the amino acid sequence of SEQ ID NO:12; and wherein theprotein binds ActRIIB; (c)(i) VH-CDR1 has the amino acid sequence of SEQID NO:23; (ii) VH-CDR2 has the amino acid sequence of SEQ ID NO:24;(iii) VH-CDR3 has the amino acid sequence of SEQ ID NO:5; (iv) VL-CDR1has the amino acid sequence of SEQ ID NO:10; (v) VL-CDR2 has the aminoacid sequence of SEQ ID NO:11; and (vi) VL-CDR3 has the amino acidsequence of SEQ ID NO:12; and wherein the protein binds ActRIIB; (d)(i)VH-CDR1 has the amino acid sequence of SEQ ID NO:29; (ii) VH-CDR2 hasthe amino acid sequence of SEQ ID NO:30; (iii) VH-CDR3 has the aminoacid sequence of SEQ ID NO:5; (iv) VL-CDR1 has the amino acid sequenceof SEQ ID NO:10; (v) VL-CDR2 has the amino acid sequence of SEQ IDNO:11; and (vi) VL-CDR3 has the amino acid sequence of SEQ ID NO:12; andwherein the protein binds ActRIIB; (e)(i) VH-CDR1 has the amino acidsequence of SEQ ID NO:35; (ii) VH-CDR2 has the amino acid sequence ofSEQ ID NO:36; (iii) VH-CDR3 has the amino acid sequence of SEQ ID NO:5;(iv) VL-CDR1 has the amino acid sequence of SEQ ID NO:10; (v) VL-CDR2has the amino acid sequence of SEQ ID NO:11; and (vi) VL-CDR3 has theamino acid sequence of SEQ ID NO:12; and wherein the protein bindsActRIIB; (f)(i) VH-CDR1 has the amino acid sequence of SEQ ID NO:41;(ii) VH-CDR2 has the amino acid sequence of SEQ ID NO: 178; (iii)VH-CDR3 has the amino acid sequence of SEQ ID NO:5; (iv) VL-CDR1 has theamino acid sequence of SEQ ID NO:10; (v) VL-CDR2 has the amino acidsequence of SEQ ID NO:11; and (vi) VL-CDR3 has the amino acid sequenceof SEQ ID NO:12; and wherein the protein binds ActRIIB; (g)(i) VH-CDR1has the amino acid sequence of SEQ ID NO:64; (ii) VH-CDR2 has the aminoacid sequence of SEQ ID NO:65; (iii) VH-CDR3 has the amino acid sequenceof SEQ ID NO:66; (iv) VL-CDR1 has the amino acid sequence of SEQ IDNO:71; (v) VL-CDR2 has the amino acid sequence of SEQ ID NO:72; and (vi)VL-CDR3 has the amino acid sequence of SEQ ID NO:73; and wherein theprotein binds ActRIIB; and (h)(i) VH-CDR1 has the amino acid sequence ofSEQ ID NO:78; (ii) VH-CDR2 has the amino acid sequence of SEQ ID NO:79;(iii) VH-CDR3 has the amino acid sequence of SEQ ID NO:80; (iv) VL-CDR1has the amino acid sequence of SEQ ID NO:71; (v) VL-CDR2 has the aminoacid sequence of SEQ ID NO:72; and (vi) VL-CDR3 has the amino acidsequence of SEQ ID NO:73; and wherein the protein binds ActRIIB; (i)(i)VH-CDR1 has the amino acid sequence of SEQ ID NO:3; (ii) VH-CDR2 has theamino acid sequence of SEQ ID NO:4; (iii) VH-CDR3 has the amino acidsequence of SEQ ID NO:46; (iv) VL-CDR1 has the amino acid sequence ofSEQ ID NO:51; (v) VL-CDR2 has the amino acid sequence of SEQ ID NO:52;and (vi) VL-CDR3 has the amino acid sequence of SEQ ID NO:53; andwherein the protein binds ActRIIB; (j)(i) VH-CDR1 has the amino acidsequence of SEQ ID NO:58; (ii) VH-CDR2 has the amino acid sequence ofSEQ ID NO:59; (iii) VH-CDR3 has the amino acid sequence of SEQ ID NO:46;(iv) VL-CDR1 has the amino acid sequence of SEQ ID NO:51; (v) VL-CDR2has the amino acid sequence of SEQ ID NO:52; and (vi) VL-CDR3 has theamino acid sequence of SEQ ID NO:53; and wherein the protein bindsActRIIB; (k)(i) VH-CDR1 has the amino acid sequence of SEQ ID NO:85;(ii) VH-CDR2 has the amino acid sequence of SEQ ID NO:86; (iii) VH-CDR3has the amino acid sequence of SEQ ID NO:87; (iv) VL-CDR1 has the aminoacid sequence of SEQ ID NO:92; (v) VL-CDR2 has the amino acid sequenceof SEQ ID NO:93; and (vi) VL-CDR3 has the amino acid sequence of SEQ IDNO:94; and wherein the protein binds ActRIIB and ActRIIA; (l)(i) VH-CDR1has the amino acid sequence of SEQ ID NO:99; (ii) VH-CDR2 has the aminoacid sequence of SEQ ID NO:100; (iii) VH-CDR3 has the amino acidsequence of SEQ ID NO:101; (iv) VL-CDR1 has the amino acid sequence ofSEQ ID NO:92; (v) VL-CDR2 has the amino acid sequence of SEQ ID NO: 153;and (vi) VL-CDR3 has the amino acid sequence of SEQ ID NO:94; andwherein the protein binds ActRIIB and ActRIIA; (m)(i) VH-CDR1 has theamino acid sequence of SEQ ID NO:106; (ii) VH-CDR2 has the amino acidsequence of SEQ ID NO:107, (iii) VH-CDR3 has the amino acid sequence ofSEQ ID NO 108; (iv) VL-CDR1 has the amino acid sequence of SEQ ID NO:92;(v) VL-CDR2 has the amino acid sequence of SEQ ID NO: 153; and (vi)VL-CDR3 has the amino acid sequence of SEQ ID NO:94; and wherein theprotein binds ActRIIB and ActRIIA; (n)(i) VH-CDR1 has the amino acidsequence of SEQ ID NO:113; (ii) VH-CDR2 has the amino acid sequence ofSEQ ID NO:114; (iii) VH-CDR3 has the amino acid sequence of SEQ IDNO:115; (iv) VL-CDR1 has the amino acid sequence of SEQ ID NO:92; (v)VL-CDR2 has the amino acid sequence of SEQ ID NO: 153; and (vi) VL-CDR3has the amino acid sequence of SEQ ID NO:94; and wherein the proteinbinds ActRIIB and ActRIIA; (o)(i) VH-CDR1 has the amino acid sequence ofSEQ ID NO:113; (ii) VH-CDR2 has the amino acid sequence of SEQ IDNO:120; (iii) VH-CDR3 has the amino acid sequence of SEQ ID NO:121; (iv)VL-CDR1 has the amino acid sequence of SEQ ID NO:92; (v) VL-CDR2 has theamino acid sequence of SEQ ID NO: 153; and (vi) VL-CDR3 has the aminoacid sequence of SEQ ID NO:94; and wherein the protein binds ActRIIB andActRIIA; or (p)(i) VH-CDR1 has the amino acid sequence of SEQ ID NO:126;(ii) VH-CDR2 has the amino acid sequence of SEQ ID NO:127; (iii) VH-CDR3has the amino acid sequence of SEQ ID NO:128; (iv) VL-CDR1 has the aminoacid sequence of SEQ ID NO:133; (v) VL-CDR2 has the amino acid sequenceof SEQ ID NO:134; and (vi) VL-CDR3 has the amino acid sequence of SEQ IDNO:135; and wherein the protein binds ActRIIA. In further aspects, theActRIIB-binding protein has at least one characteristic selected fromthe group consisting of: (a) competes with an ActRII ligand (e.g.,activin A, activin B, GDF1, GDF3, GDF8 (myostatin), GDF11, BMP6, BMP7,BMP9, or BMP10) for binding to ActRII; (b) decreases the phosphorylationof Smads (e.g., Smad2 and/or Smad3) in cells expressing ActRII in thepresence of an ActRII ligand (e.g., activin A or GDF8); (c) decreasesthe phosphorylation of ALK4 and/or ALK7 in cells expressing ActRII andALK4 and/or ALK7 in the presence of an ActRII ligand; and (d) binds toActRII with a K_(D) of ≤1 nM and ≥1 pM (e.g., as determined by BIACORE®analysis). In some aspects, the ActRII-binding protein has 2, 3, or 4 ofthe above characteristics. In some aspects, the ActRII-binding proteinhas at least 2 or at least 3 of the above characteristics.

In some aspects, an ActRII-binding protein specifically binds ActRIIBand comprises a set of CDRs: VH-CDR1, VH-CDR2, and VH-CDR3, wherein theset of CDRs is identical to, or has a total of one, two, three, four,five, six, seven, eight, nine, ten, or fewer than ten, amino acidsubstitutions, deletions, and/or insertions from a reference set of CDRsin which: (a)(i) VH-CDR1 has the amino acid sequence of SEQ ID NO:3, 17,23, 29, 35, or 41; (ii) VH-CDR2 has the amino acid sequence of SEQ IDNO:4, 18, 24, 30, 178, or 36; and (iii) VH-CDR3 has the amino acidsequence of SEQ ID NO:5; (b)(i) VH-CDR1 has the amino acid sequence ofSEQ ID NO:3 or 58; (ii) VH-CDR2 has the amino acid sequence of SEQ IDNO:4 or 59; and (iii) VH-CDR3 has the amino acid sequence of SEQ IDNO:46; or (c)(i) VH-CDR1 has the amino acid sequence of SEQ ID NO:64 or78; (ii) VH-CDR2 has the amino acid sequence of SEQ ID NO:65 or 79; and(iii) VH-CDR3 has the amino acid sequence of SEQ ID NO:66 or 80. Infurther aspects, the ActRIIB-binding protein has at least onecharacteristic selected from the group consisting of: (a) competes withan ActRII ligand (e.g., activin A, activin B, GDF1, GDF3, GDF8(myostatin), GDF11, BMP6, BMP7, BMP9, or BMP10) for binding to ActRIIB;(b) decreases the phosphorylation of Smads (e.g., Smad2 and/or Smad3) incells expressing ActRIIB in the presence of an ActRIIB ligand (e.g.,activin A or GDF8); (c) decreases the phosphorylation of ALK4 and/orALK7 in cells expressing ActRIIB and ALK4 and/or ALK7 in the presence ofan ActRIIB ligand; and (d) binds to ActRIIB with a K_(D) of ≤1 nM and ≥1pM (e.g., as determined by BIACORE® analysis). In some aspects, theActRIIB-binding protein has 2, 3, or 4 of the above characteristics. Insome aspects, the ActRIIB-binding protein has at least 2 or at least 3of the above characteristics.

In some aspects, an ActRII-binding protein specifically binds ActRIIBand comprises a set of CDRs: VH-CDR1, VH-CDR2, and VH-CDR3, wherein theset of CDRs is identical to, or has a total of one, two, three, four,five, six, seven, eight, nine, ten, or fewer than ten, amino acidsubstitutions, deletions, and/or insertions from a reference set of CDRsin which: (a)(i) VH-CDR1 has the amino acid sequence of SEQ ID NO:3;(ii) VH-CDR2 has the amino acid sequence of SEQ ID NO:4; (iii) VH-CDR3has the amino acid sequence of SEQ ID NO:5; and wherein the proteinbinds ActRIIB; (b)(i) VH-CDR1 has the amino acid sequence of SEQ IDNO:17; (ii) VH-CDR2 has the amino acid sequence of SEQ ID NO:18; (iii)VH-CDR3 has the amino acid sequence of SEQ ID NO:5; and wherein theprotein binds ActRIIB; (c)(i) VH-CDR1 has the amino acid sequence of SEQID NO:23; (ii) VH-CDR2 has the amino acid sequence of SEQ ID NO:24;(iii) VH-CDR3 has the amino acid sequence of SEQ ID NO:5; and whereinthe protein binds ActRIIB; (d)(i) VH-CDR1 has the amino acid sequence ofSEQ ID NO:29; (ii) VH-CDR2 has the amino acid sequence of SEQ ID NO:30;(iii) VH-CDR3 has the amino acid sequence of SEQ ID NO:5; and whereinthe protein binds ActRIIB; (e)(i) VH-CDR1 has the amino acid sequence ofSEQ ID NO:35; (ii) VH-CDR2 has the amino acid sequence of SEQ ID NO:36;(iii) VH-CDR3 has the amino acid sequence of SEQ ID NO:5; and whereinthe protein binds ActRIIB; (f)(i) VH-CDR1 has the amino acid sequence ofSEQ ID NO:41; (ii) VH-CDR2 has the amino acid sequence of SEQ ID NO:178; (iii) VH-CDR3 has the amino acid sequence of SEQ ID NO:5; andwherein the protein binds ActRIIB; (g)(i) VH-CDR1 has the amino acidsequence of SEQ ID NO:64; (ii) VH-CDR2 has the amino acid sequence ofSEQ ID NO:65; (iii) VH-CDR3 has the amino acid sequence of SEQ ID NO:66;and wherein the protein binds ActRIIB; (h)(i) VH-CDR1 has the amino acidsequence of SEQ ID NO:78; (ii) VH-CDR2 has the amino acid sequence ofSEQ ID NO:79; (iii) VH-CDR3 has the amino acid sequence of SEQ ID NO:80;and wherein the protein binds ActRIIB; (i)(i) VH-CDR1 has the amino acidsequence of SEQ ID NO:3; (ii) VH-CDR2 has the amino acid sequence of SEQID NO:4; (iii) VH-CDR3 has the amino acid sequence of SEQ ID NO:46; andwherein the protein binds ActRIIB; or (j)(i) VH-CDR1 has the amino acidsequence of SEQ ID NO:58; (ii) VH-CDR2 has the amino acid sequence ofSEQ ID NO:59; (iii) VH-CDR3 has the amino acid sequence of SEQ ID NO:46;and wherein the protein binds ActRIIB. In further aspects, theActRIIB-binding protein has at least one characteristic selected fromthe group consisting of: (a) competes with an ActRII ligand (e.g.,activin A, activin B, GDF1, GDF3, GDF8 (myostatin), GDF11, BMP6, BMP7,BMP9, or BMP10) for binding to ActRIIB; (b) decreases thephosphorylation of Smads (e.g., Smad2 and/or Smad3) in cells expressingActRIIB in the presence of an ActRIIB ligand (e.g., activin A or GDF8);(c) decreases the phosphorylation of ALK4 and/or ALK7 in cellsexpressing ActRIIB and ALK4 and/or ALK7 in the presence of an ActRIIBligand; and (d) binds to ActRIIB with a K_(D) of ≤1 nM and ≥1 pM (e.g.,as determined by BIACORE® analysis). In some aspects, theActRIIB-binding protein has 2, 3, or 4 of the above characteristics. Insome aspects, the ActRIIB-binding protein has at least 2 or at least 3of the above characteristics.

In some aspects, an ActRII-binding protein specifically binds ActRIIBand comprises a set of CDRs: VL-CDR1, VL-CDR2, and VL-CDR3, wherein theset of CDRs is identical to, or has a total of one, two, three, four,five, six, seven, eight, nine, ten, or fewer than ten, amino acidsubstitutions, deletions, and/or insertions from a reference set of CDRsin which: (a)(i) VL-CDR1 has the amino acid sequence of SEQ ID NO:10;(ii) VL-CDR2 has the amino acid sequence of SEQ ID NO:11; and (iii)VL-CDR3 has the amino acid sequence of SEQ ID NO:12; and wherein theprotein binds ActRIIB; (b)(i) VL-CDR1 has the amino acid sequence of SEQID NO:71; (ii) VL-CDR2 has the amino acid sequence of SEQ ID NO:72; and(iii) VL-CDR3 has the amino acid sequence of SEQ ID NO:73; and whereinthe protein binds ActRIIB; or (c)(i) VL-CDR1 has the amino acid sequenceof SEQ ID NO:51; (ii) VL-CDR2 has the amino acid sequence of SEQ IDNO:52; and (iii) VL-CDR3 has the amino acid sequence of SEQ ID NO:53;and wherein the protein binds ActRIIB. In further aspects, theActRIIB-binding protein has at least one characteristic selected fromthe group consisting of: (a) competes with an ActRII ligand (e.g.,activin A, activin B, GDF1, GDF3, GDF8 (myostatin), GDF11, BMP6, BMP7,BMP9, or BMP10) for binding to ActRIIB; (b) decreases thephosphorylation of Smads (e.g., Smad2 and/or Smad3) in cells expressingActRIIB in the presence of an ActRIIB ligand (e.g., activin A or GDF8);(c) decreases the phosphorylation of ALK4 and/or ALK7 in cellsexpressing ActRIIB and ALK4 and/or ALK7 in the presence of an ActRIIBligand; and (d) binds to ActRIIB with a K_(D) of ≤1 nM and ≥1 pM (e.g.,as determined by BIACORE® analysis). In some aspects, theActRIIB-binding protein has 2, 3, or 4 of the above characteristics. Insome aspects, the ActRIIB-binding protein has at least 2 or at least 3of the above characteristics.

In some aspects, an ActRII-binding protein specifically binds ActRIIBand ActRIIA and comprises a set of CDRs: VH-CDR1, VH-CDR2, and VH-CDR3,wherein the set of CDRs is identical to, or has a total of one, two,three, four, five, six, seven, eight, nine, ten, or fewer than ten,amino acid substitutions, deletions, and/or insertions from a referenceset of CDRs in which VH-CDR1 has the amino acid sequence of SEQ IDNO:85, 99, 106, or 113; VH-CDR2 has the amino acid sequence of SEQ IDNO:86, 100, 107, 114, or 120; and VH-CDR3 has the amino acid sequence ofSEQ ID NO:87, 101, 108, 115, or 121. In further aspects, the ActRIIB-and ActRIIA-binding protein has at least one characteristic selectedfrom the group consisting of: (a) competes with an ActRII ligand (e.g.,activin A, activin B, GDF1, GDF3, GDF8 (myostatin), GDF11, BMP6, BMP7,BMP9, or BMP10) for binding to ActRIIB and/or ActRIIA; (b) decreases thephosphorylation of Smads (e.g., Smad2 and/or Smad3) in cells expressingActRIIB and/or ActRIIA in the presence of an ActRIIB and/or ActRIIAligand (e.g., activin A or GDF8); (c) decreases the phosphorylation ofALK4 and/or ALK7 in cells expressing ActRIIB and/or ActRIIA and ALK4and/or ALK7 in the presence of an ActRIIB and/or ActRIIA ligand; and (d)binds to ActRIIB and/or ActRIIA with a K_(D) of ≤1 nM and ≥1 pM (e.g.,as determined by BIACORE® analysis). In some aspects, the ActRIIB and/orActRIIA-binding protein has 2, 3, or 4 of the above characteristics. Insome aspects, the ActRIIB and/or ActRIIA-binding protein has at least 2or at least 3 of the above characteristics.

In some aspects, an ActRII-binding protein specifically binds ActRIIBand ActRIIA and comprises a set of CDRs: VH-CDR1, VH-CDR2, and VH-CDR3,wherein the set of CDRs is identical to, or has a total of one, two,three, four, five, six, seven, eight, nine, ten, or fewer than ten,amino acid substitutions, deletions, and/or insertions from a referenceset of CDRs in which: (a)(i) VH-CDR1 has the amino acid sequence of SEQID NO:85; (ii) VH-CDR2 has the amino acid sequence of SEQ ID NO:86;(iii) VH-CDR3 has the amino acid sequence of SEQ ID NO:87; and whereinthe protein binds ActRIIB and ActRIIA; (b)(i) VH-CDR1 has the amino acidsequence of SEQ ID NO:99; (ii) VH-CDR2 has the amino acid sequence ofSEQ ID NO:100; (iii) VH-CDR3 has the amino acid sequence of SEQ IDNO:101; and wherein the protein binds ActRIIB and ActRIIA; (c)(i)VH-CDR1 has the amino acid sequence of SEQ ID NO:106; (ii) VH-CDR2 hasthe amino acid sequence of SEQ ID NO:107, (iii) VH-CDR3 has the aminoacid sequence of SEQ ID NO 108; and wherein the protein binds ActRIIBand ActRIIA; (d)(i) VH-CDR1 has the amino acid sequence of SEQ IDNO:113; (ii) VH-CDR2 has the amino acid sequence of SEQ ID NO:114; (iii)VH-CDR3 has the amino acid sequence of SEQ ID NO:115; and wherein theprotein binds ActRIIB and ActRIIA; or (e)(i) VH-CDR1 has the amino acidsequence of SEQ ID NO:113; (ii) VH-CDR2 has the amino acid sequence ofSEQ ID NO:120; (iii) VH-CDR3 has the amino acid sequence of SEQ IDNO:121; and wherein the protein binds ActRIIB and ActRIIA. In furtheraspects, the ActRII-binding protein has at least one characteristicselected from the group consisting of: (a) competes with an ActRIIligand (e.g., activin A, activin B, GDF1, GDF3, GDF8 (myostatin), GDF11,BMP6, BMP7, BMP9, or BMP10) for binding to ActRIIB and/or ActRIIA; (b)decreases the phosphorylation of Smads (e.g., Smad2 and/or Smad3) incells expressing ActRIIB and/or ActRIIA in the presence of an ActRIIBand/or ActRIIA ligand (e.g., activin A or GDF8); (c) decreases thephosphorylation of ALK4 and/or ALK7 in cells expressing ActRIIB and/orActRIIA and ALK4 and/or ALK7 in the presence of an ActRIIB and/orActRIIA ligand; and (d) binds to ActRIIB and/or ActRIIA with a K_(D) of≤1 nM and ≥1 pM (e.g., as determined by BIACORE® analysis). In someaspects, the ActRIIB and/or ActRIIA-binding protein has 2, 3, or 4 ofthe above characteristics. In some aspects, the ActRIIB and/orActRIIA-binding protein has at least 2 or at least 3 of the abovecharacteristics.

In some aspects, an ActRII-binding protein specifically binds ActRIIBand ActRIIA and comprises a set of CDRs: VL-CDR1, VL-CDR2, and VL-CDR3,wherein the set of CDRs is identical to, or has a total of one, two,three, four, five, six, seven, eight, nine, ten, or fewer than ten,amino acid substitutions, deletions, and/or insertions from a referenceset of CDRs in which VL-CDR1 has the amino acid sequence of SEQ IDNO:92; (ii) VL-CDR2 has the amino acid sequence of SEQ ID NO:93; and(iii) VL-CDR3 has the amino acid sequence of SEQ ID NO:94; and whereinthe protein binds ActRIIB and ActRIIA. In further aspects, theActRII-binding protein has at least one characteristic selected from thegroup consisting of: (a) competes with an ActRII ligand (e.g., activinA, activin B, GDF1, GDF3, GDF8 (myostatin), GDF11, BMP6, BMP7, BMP9, orBMP10) for binding to ActRIIB and/or ActRIIA; (b) decreases thephosphorylation of Smads (e.g., Smad2 and/or Smad3) in cells expressingActRIIB and/or ActRIIA in the presence of an ActRIIB and/or ActRIIAligand (e.g., activin A or GDF8); (c) decreases the phosphorylation ofALK4 and/or ALK7 in cells expressing ActRIIB and/or ActRIIA and ALK4and/or ALK7 in the presence of an ActRIIB and/or ActRIIA ligand; and (d)binds to ActRIIB and/or ActRIIA with a K_(D) of ≤1 nM and ≥1 pM (e.g.,as determined by BIACORE® analysis). In some aspects, the ActRIIB and/orActRIIA-binding protein has 2, 3, or 4 of the above characteristics. Insome aspects, the ActRIIB and/or ActRIIA-binding protein has at least 2or at least 3 of the above characteristics.

In some aspects, an ActRII-binding protein specifically binds ActRIIAand comprises a set of CDRs: VH-CDR1, VH-CDR2, and VH-CDR3, wherein theset of CDRs is identical to, or has a total of one, two, three, four,five, six, seven, eight, nine, ten, or fewer than ten, amino acidsubstitutions, deletions, and/or insertions from a reference set of CDRsin which VH-CDR1 has the amino acid sequence of SEQ ID NO:126; VH-CDR2has the amino acid sequence of SEQ ID NO:127; and VH-CDR3 has the aminoacid sequence of SEQ ID NO:128. In further aspects, the ActRIIA-bindingprotein has at least one characteristic selected from the groupconsisting of (a) competes with an ActRIIA ligand (e.g., activin A,activin B, GDF1, GDF3, or Nodal); (b) decreases the phosphorylation ofSmads (e.g., Smad2 and/or Smad3) in cells expressing ActRIIA in thepresence of an ActRIIA ligand (e.g., activin A); (c) decreases thephosphorylation of ALK4 and/or ALK7 in cells expressing ActRIIA and ALK4and/or ALK7 in the presence of an ActRIIA ligand; and (d) binds toActRIIA with a K_(D) of ≤1 nM and ≥1 pM (e.g., as determined by BIACORE®analysis). In some aspects, the ActRIIA-binding protein has 2, 3, or 4of the above characteristics. In some aspects, the ActRIIA-bindingprotein has at least 2 or at least 3 of the above characteristics.

In some aspects, the ActRII-binding protein specifically binds ActRIIAand comprises a set of CDRs: VL-CDR1, VL-CDR2, and VL-CDR3, wherein theset of CDRs is identical to, or has a total of one, two, three, four,five, six, seven, eight, nine, ten, or fewer than ten, amino acidsubstitutions, deletions, and/or insertions from a reference set of CDRsin which: VL-CDR1 has the amino acid sequence of SEQ ID NO:133 VL-CDR2has the amino acid sequence of SEQ ID NO:134; and VL-CDR3 has the aminoacid sequence of SEQ ID NO:135. In further aspects, the ActRIIA-bindingprotein has at least one characteristic selected from the groupconsisting of (a) competes with an ActRIIA ligand (e.g., activin A,activin B, GDF1, GDF3, or Nodal); (b) decreases the phosphorylation ofSmads (e.g., Smad2 and/or Smad3) in cells expressing ActRIIA in thepresence of an ActRIIA ligand (e.g., activin A); (c) decreases thephosphorylation of ALK4 and/or ALK7 in cells expressing ActRIIA and ALK4and/or ALK7 in the presence of an ActRIIA ligand; and (d) binds toActRIIA with a K_(D) of ≤1 nM and ≥1 pM (e.g., as determined by BIACORE®analysis). In some aspects, the ActRIIA-binding protein has 2, 3, or 4of the above characteristics. In some aspects, the ActRIIA-bindingprotein has at least 2 or at least 3 of the above characteristics.

In additional aspects, the ActRII-binding protein specifically bindsActRIIB and comprises a set of CDRs: VH-CDR1, VH-CDR2, VH-CDR3, VL-CDR1,VL-CDR2, and VL-CDR3, wherein the set of CDRs is identical to, or has atotal of one, two, three, four, five, six, seven, eight, nine, ten, orfewer than ten, amino acid substitutions, deletions, and/or insertionsfrom a reference set of CDRs in which: (a)(i) VH-CDR1 has the amino acidsequence of SEQ ID NO:3, 17, 23, 29, 35, or 41; (ii) VH-CDR2 has theamino acid sequence of SEQ ID NO:4, 18, 24, 30, 178, or 36; (iii)VH-CDR3 has the amino acid sequence of SEQ ID NO:5; (iv) VL-CDR1 has theamino acid sequence of SEQ ID NO:10; (v) VL-CDR2 has the amino acidsequence of SEQ ID NO:11; or (vi) VL-CDR3 has the amino acid sequence ofSEQ ID NO:12; (b)(i) VH-CDR1 has the amino acid sequence of SEQ ID NO:3or 58; (ii) VH-CDR2 has the amino acid sequence of SEQ ID NO:4 or 59;(iii) VH-CDR3 has the amino acid sequence of SEQ ID NO:46; (iv) VL-CDR1has the amino acid sequence of SEQ ID NO:51; (v) VL-CDR2 has the aminoacid sequence of SEQ ID NO:52; or (vi) VL-CDR3 has the amino acidsequence of SEQ ID NO:53; or (c)(i) VH-CDR1 has the amino acid sequenceof SEQ ID NO:64 or 78; (ii) VH-CDR2 has the amino acid sequence of SEQID NO:65 or 79; (iii) VH-CDR3 has the amino acid sequence of SEQ IDNO:66, or 80; (iv) VL-CDR1 has the amino acid sequence of SEQ ID NO:71;(v) VL-CDR2 has the amino acid sequence of SEQ ID NO:72; or (vi) VL-CDR3has the amino acid sequence of SEQ ID NO:73. In further aspects, theActRIIB-binding protein comprises a VH and a VL. In further aspects, theActRIIB-binding protein has at least one characteristic selected fromthe group consisting of (a) competes with an ActRII ligand (e.g.,activin A, activin B, GDF1, GDF3, GDF8 (myostatin), GDF11, BMP6, BMP7,BMP9, or BMP10) for binding to ActRIIB; (b) decreases thephosphorylation of Smads (e.g., Smad2 and/or Smad3) in cells expressingActRIIB in the presence of an ActRIIB ligand (e.g., activin A or GDF8);(c) decreases the phosphorylation of ALK4 and/or ALK7 in cellsexpressing ActRIIB and ALK4 and/or ALK7 in the presence of an ActRIIBligand; and (d) binds to ActRIIB with a K_(D) of ≤1 nM and ≥1 pM (e.g.,as determined by BIACORE® analysis). In some aspects, theActRIIB-binding protein has 2, 3, or 4 of the above characteristics. Insome aspects, the ActRIIB-binding protein has at least 2 or at least 3of the above characteristics.

In further aspects, the ActRII-binding protein specifically bindsActRIIB and comprises a set of CDRs: VH-CDR1, VH-CDR2, VH-CDR3, VL-CDR1,VL-CDR2, and VL-CDR3, wherein: (a)(i) VH-CDR1 has the amino acidsequence of SEQ ID NO:3, 17, 23, 29, 35, or 41; (ii) VH-CDR2 has theamino acid sequence of SEQ ID NO:4, 18, 24, 30, 178, or 36; (iii)VH-CDR3 has the amino acid sequence of SEQ ID NO:5; (iv) VL-CDR1 has theamino acid sequence of SEQ ID NO:10; (v) VL-CDR2 has the amino acidsequence of SEQ ID NO:11; or (vi) VL-CDR3 has the amino acid sequence ofSEQ ID NO:12; (b)(i) VH-CDR1 has the amino acid sequence of SEQ ID NO:3or 58; (ii) VH-CDR2 has the amino acid sequence of SEQ ID NO:4 or 59;(iii) VH-CDR3 has the amino acid sequence of SEQ ID NO:46; (iv) VL-CDR1has the amino acid sequence of SEQ ID NO:51; (v) VL-CDR2 has the aminoacid sequence of SEQ ID NO:52; or (vi) VL-CDR3 has the amino acidsequence of SEQ ID NO:53; or (c)(i) VH-CDR1 has the amino acid sequenceof SEQ ID NO:64 or 78; (ii) VH-CDR2 has the amino acid sequence of SEQID NO:65 or 79; (iii) VH-CDR3 has the amino acid sequence of SEQ IDNO:66, or 80; (iv) VL-CDR1 has the amino acid sequence of SEQ ID NO:71;(v) VL-CDR2 has the amino acid sequence of SEQ ID NO:72; or (vi) VL-CDR3has the amino acid sequence of SEQ ID NO:73. In further aspects, theActRIIB-binding protein comprises a VH and a VL. In further aspects, theActRIIB-binding protein has at least one characteristic selected fromthe group consisting of (a) competes with an ActRII ligand (e.g.,activin A, activin B, GDF1, GDF3, GDF8 (myostatin), GDF11, BMP6, BMP7,BMP9, or BMP10) for binding to ActRIIB; (b) decreases thephosphorylation of Smads (e.g., Smad2 and/or Smad3) in cells expressingActRIIB in the presence of an ActRIIB ligand (e.g., activin A or GDF8);(c) decreases the phosphorylation of ALK4 and/or ALK7 in cellsexpressing ActRIIB and ALK4 and/or ALK7 in the presence of an ActRIIBligand; and (d) binds to ActRIIB with a K_(D) of ≤1 nM and ≥1 pM (e.g.,as determined by BIACORE® analysis). In some aspects, theActRIIB-binding protein has 2, 3, or 4 of the above characteristics. Insome aspects, the ActRIIB-binding protein has at least 2 or at least 3of the above characteristics.

In additional aspects, the ActRII-binding protein specifically bindsActRIIB and ActRIIA and comprises a set of CDRs: VH-CDR1, VH-CDR2,VH-CDR3, VL-CDR1, VL-CDR2, and VL-CDR3, wherein the set of CDRs isidentical to, or has a total of one, two, three, four, five, six, seven,eight, nine, ten, or fewer than ten, amino acid substitutions,deletions, and/or insertions from a reference set of CDRs in which: (a)VH-CDR1 has the amino acid sequence of SEQ ID NO:85, 99, 106 166, or113; (b) VH-CDR2 has the amino acid sequence of SEQ ID NO:86, 100, 107,114, 167, or 120; (c) VH-CDR3 has the amino acid sequence of SEQ IDNO:87, 101, 108, 115, 168, or 121; (d) VL-CDR1 has the amino acidsequence of SEQ ID NO:92, or 173; (e) VL-CDR2 has the amino acidsequence of SEQ ID NO:93, 153, or 174; or (f) VL-CDR3 has the amino acidsequence of SEQ ID NO:94, or 175. In further aspects, the ActRII-bindingprotein has at least one characteristic selected from the groupconsisting of: (a) competes with an ActRII ligand (e.g., activin A,activin B, GDF1, GDF3, GDF8 (myostatin), GDF11, BMP6, BMP7, BMP9, orBMP10) for binding to ActRIIB and/or ActRIIA; (b) decreases thephosphorylation of Smads (e.g., Smad2 and/or Smad3) in cells expressingActRIIB and/or ActRIIA in the presence of an ActRIIB and/or ActRIIAligand (e.g., activin A or GDF8); (c) decreases the phosphorylation ofALK4 and/or ALK7 in cells expressing ActRIIB and/or ActRIIA and ALK4and/or ALK7 in the presence of an ActRIIB and/or ActRIIA ligand; and (d)binds to ActRIIB and/or ActRIIA with a K_(D) of ≤1 nM and ≥1 pM (e.g.,as determined by BIACORE® analysis). In some aspects, the ActRIIB and/orActRIIA-binding protein has 2, 3, or 4 of the above characteristics. Insome aspects, the ActRIIB and/or ActRIIA-binding protein has at least 2or at least 3 of the above characteristics.

In additional aspects, the ActRII-binding protein specifically bindsActRIIB and ActRIIA and comprises a set of CDRs: VH-CDR1, VH-CDR2,VH-CDR3, VL-CDR1, VL-CDR2, and VL-CDR3, wherein: (a) VH-CDR1 has theamino acid sequence of SEQ ID NO:85, 99, 106 166, or 113; (b) VH-CDR2has the amino acid sequence of SEQ ID NO:86, 100, 107, 114, 167, or 120;(c) VH-CDR3 has the amino acid sequence of SEQ ID NO:87, 101, 108, 115,168, or 121; (d) VL-CDR1 has the amino acid sequence of SEQ ID NO:92, or173; (e) VL-CDR2 has the amino acid sequence of SEQ ID NO:93, 153, or174; or (f) VL-CDR3 has the amino acid sequence of SEQ ID NO:94, or 175.In further aspects, the ActRII-binding protein has at least onecharacteristic selected from the group consisting of: (a) competes withan ActRII ligand (e.g., activin A, activin B, GDF1, GDF3, GDF8(myostatin), GDF11, BMP6, BMP7, BMP9, or BMP10) for binding to ActRIIBand/or ActRIIA; (b) decreases the phosphorylation of Smads (e.g., Smad2and/or Smad3) in cells expressing ActRIIB and/or ActRIIA in the presenceof an ActRIIB and/or ActRIIA ligand (e.g., activin A or GDF8); (c)decreases the phosphorylation of ALK4 and/or ALK7 in cells expressingActRIIB and/or ActRIIA and ALK4 and/or ALK7 in the presence of anActRIIB and/or ActRIIA ligand; and (d) binds to ActRIIB and/or ActRIIAwith a K_(D) of ≤1 nM and ≥1 pM (e.g., as determined by BIACORE®analysis). In some aspects, the ActRIIB and/or ActRIIA-binding proteinhas 2, 3, or 4 of the above characteristics. In some aspects, theActRIIB and/or ActRIIA-binding protein has at least 2 or at least 3 ofthe above characteristics.

In additional aspects, the ActRII-binding protein specifically bindsActRIIA and comprises a set of CDRs: VH-CDR1, VH-CDR2, VH-CDR3, VL-CDR1,VL-CDR2, and VL-CDR3, wherein the set of CDRs is identical to, or has atotal of one, two, three, four, five, six, seven, eight, nine, ten, orfewer than ten, amino acid substitutions, deletions, and/or insertionsfrom a reference set of CDRs in which: (a) VH-CDR1 has the amino acidsequence of SEQ ID NO:126; (b) VH-CDR2 has the amino acid sequence ofSEQ ID NO:127; (c) VH-CDR3 has the amino acid sequence of SEQ ID NO:128;(d) VL-CDR1 has the amino acid sequence of SEQ ID NO:133; (e) VL-CDR2has the amino acid sequence of SEQ ID NO:134; or (f) VL-CDR3 has theamino acid sequence of SEQ ID NO:135. In further aspects, theActRIIA-binding protein has at least one characteristic selected fromthe group consisting of (a) competes with an ActRIIA ligand (e.g.,activin A, activin B, GDF1, GDF3, or Nodal); (b) decreases thephosphorylation of Smads (e.g., Smad2 and/or Smad3) in cells expressingActRIIA in the presence of an ActRIIA ligand (e.g., activin A); (c)decreases the phosphorylation of ALK4 and/or ALK7 in cells expressingActRIIA and ALK4 and/or ALK7 in the presence of an ActRIIA ligand; and(d) binds to ActRIIA with a K_(D) of ≤1 nM and ≥1 pM (e.g., asdetermined by BIACORE® analysis). In some aspects, the ActRIIA-bindingprotein has 2, 3, or 4 of the above characteristics. In some aspects,the ActRIIA-binding protein has at least 2 or at least 3 of the abovecharacteristics.

In further aspects, the ActRII-binding protein specifically bindsActRIIA and comprises a set of CDRs: VH-CDR1, VH-CDR2, VH-CDR3, VL-CDR1,VL-CDR2, and VL-CDR3, wherein: (a) VH-CDR1 has the amino acid sequenceof SEQ ID NO:126; (b) VH-CDR2 has the amino acid sequence of SEQ IDNO:127; (c) VH-CDR3 has the amino acid sequence of SEQ ID NO:128; (d)VL-CDR1 has the amino acid sequence of SEQ ID NO:133; (e) VL-CDR2 hasthe amino acid sequence of SEQ ID NO:134; or (f) VL-CDR3 has the aminoacid sequence of SEQ ID NO:135. In further aspects, the ActRIIA-bindingprotein has at least one characteristic selected from the groupconsisting of (a) competes with an ActRIIA ligand (e.g., activin A,activin B, GDF1, GDF3, or Nodal); (b) decreases the phosphorylation ofSmads (e.g., Smad2 and/or Smad3) in cells expressing ActRIIA in thepresence of an ActRIIA ligand (e.g., activin A); (c) decreases thephosphorylation of ALK4 and/or ALK7 in cells expressing ActRIIA and ALK4and/or ALK7 in the presence of an ActRIIA ligand; and (d) binds toActRIIA with a K_(D) of ≤1 nM and ≥1 pM (e.g., as determined by BIACORE®analysis). In some aspects, the ActRIIA-binding protein has 2, 3, or 4of the above characteristics. In some aspects, the ActRIIA-bindingprotein has at least 2 or at least 3 of the above characteristics.

In some aspects, the ActRII-binding protein specifically binds ActRIIand comprises a set of CDRs in which: (a)(i) VH-CDR1 has the amino acidsequence of SEQ ID NO:3, 17, 23, 29, 35 or 41; (ii) VH-CDR2 has theamino acid sequence of SEQ ID NO:4, 18, 24, 30, 178, or 36; (iii)VH-CDR3 has the amino acid sequence of SEQ ID NO:5; (iv) VL-CDR1 has theamino acid sequence of SEQ ID NO:10; (v) VL-CDR2 has the amino acidsequence of SEQ ID NO:11; and (vi) VL-CDR3 has the amino acid sequenceof SEQ ID NO:12; and wherein the protein binds ActRIIB; (b)(i) VH-CDR1has the amino acid sequence of SEQ ID NO:64 or 78; (ii) VH-CDR2 has theamino acid sequence of SEQ ID NO:65 or 79; (iii) VH-CDR3 has the aminoacid sequence of SEQ ID NO:66 or 80; (iv) VL-CDR1 has the amino acidsequence of SEQ ID NO:71; (v) VL-CDR2 has the amino acid sequence of SEQID NO:72; and (vi) VL-CDR3 has the amino acid sequence of SEQ ID NO:73;and wherein the protein binds ActRIIB; (c)(i) VH-CDR1 has the amino acidsequence of SEQ ID NO:3 or 58; (ii) VH-CDR2 has the amino acid sequenceof SEQ ID NO:4 or 59; (iii) VH-CDR3 has the amino acid sequence of SEQID NO:46; (iv) VL-CDR1 has the amino acid sequence of SEQ ID NO:51; (v)VL-CDR2 has the amino acid sequence of SEQ ID NO:52; and (vi) VL-CDR3has the amino acid sequence of SEQ ID NO:53; and wherein the proteinbinds ActRIIB; (d)(i) VH-CDR1 has the amino acid sequence of SEQ IDNO:85, 99, 106, 166, or 113; (ii) VH-CDR2 has the amino acid sequence ofSEQ ID NO:86, 100, 107, 114, 167, or 120; (iii) VH-CDR3 has the aminoacid sequence of SEQ ID NO:87, 101, 108, 115, 168, or 121; (iv) VL-CDR1has the amino acid sequence of SEQ ID NO:92, or 173; (v) VL-CDR2 has theamino acid sequence of SEQ ID NO:93, 153, or 174; and (vi) VL-CDR3 hasthe amino acid sequence of SEQ ID NO:94, or 175; and wherein the proteinbinds ActRIIB and ActRIIA; or (e)(i) VH-CDR1 has the amino acid sequenceof SEQ ID NO:126; (ii) VH-CDR2 has the amino acid sequence of SEQ IDNO:127; (iii) VH-CDR3 has the amino acid sequence of SEQ ID NO:128; (iv)VL-CDR1 has the amino acid sequence of SEQ ID NO:133; (v) VL-CDR2 hasthe amino acid sequence of SEQ ID NO:134; and (vi) VL-CDR3 has the aminoacid sequence of SEQ ID NO:135; and wherein the protein binds ActRIIA.

In additional aspects, the ActRII-binding protein comprises a set ofCDRs in which: (a)(i) VH-CDR1 has the amino acid sequence of SEQ IDNO:3; (ii) VH-CDR2 has the amino acid sequence of SEQ ID NO:4; (iii)VH-CDR3 has the amino acid sequence of SEQ ID NO:5; (iv) VL-CDR1 has theamino acid sequence of SEQ ID NO:10; (v) VL-CDR2 has the amino acidsequence of SEQ ID NO:11; and (vi) VL-CDR3 has the amino acid sequenceof SEQ ID NO:12; and wherein the protein binds ActRIIB; (b)(i) VH-CDR1has the amino acid sequence of SEQ ID NO:17; (ii) VH-CDR2 has the aminoacid sequence of SEQ ID NO:18; (iii) VH-CDR3 has the amino acid sequenceof SEQ ID NO:5; (iv) VL-CDR1 has the amino acid sequence of SEQ IDNO:10; (v) VL-CDR2 has the amino acid sequence of SEQ ID NO:11; and (vi)VL-CDR3 has the amino acid sequence of SEQ ID NO:12; and wherein theprotein binds ActRIIB; (c)(i) VH-CDR1 has the amino acid sequence of SEQID NO:23; (ii) VH-CDR2 has the amino acid sequence of SEQ ID NO:24;(iii) VH-CDR3 has the amino acid sequence of SEQ ID NO:5; (iv) VL-CDR1has the amino acid sequence of SEQ ID NO:10; (v) VL-CDR2 has the aminoacid sequence of SEQ ID NO:11; and (vi) VL-CDR3 has the amino acidsequence of SEQ ID NO:12; and wherein the protein binds ActRIIB; (d)(i)VH-CDR1 has the amino acid sequence of SEQ ID NO:29; (ii) VH-CDR2 hasthe amino acid sequence of SEQ ID NO:30; (iii) VH-CDR3 has the aminoacid sequence of SEQ ID NO:5; (iv) VL-CDR1 has the amino acid sequenceof SEQ ID NO:10; (v) VL-CDR2 has the amino acid sequence of SEQ IDNO:11; and (vi) VL-CDR3 has the amino acid sequence of SEQ ID NO:12; andwherein the protein binds ActRIIB; (e)(i) VH-CDR1 has the amino acidsequence of SEQ ID NO:35; (ii) VH-CDR2 has the amino acid sequence ofSEQ ID NO:36; (iii) VH-CDR3 has the amino acid sequence of SEQ ID NO:5;(iv) VL-CDR1 has the amino acid sequence of SEQ ID NO:10; (v) VL-CDR2has the amino acid sequence of SEQ ID NO:11; and (vi) VL-CDR3 has theamino acid sequence of SEQ ID NO:12; and wherein the protein bindsActRIIB; (f)(i) VH-CDR1 has the amino acid sequence of SEQ ID NO:41;(ii) VH-CDR2 has the amino acid sequence of SEQ ID NO: 178; (iii)VH-CDR3 has the amino acid sequence of SEQ ID NO:5; (iv) VL-CDR1 has theamino acid sequence of SEQ ID NO:10; (v) VL-CDR2 has the amino acidsequence of SEQ ID NO:11; and (vi) VL-CDR3 has the amino acid sequenceof SEQ ID NO:12; and wherein the protein binds ActRIIB; (g)(i) VH-CDR1has the amino acid sequence of SEQ ID NO:64; (ii) VH-CDR2 has the aminoacid sequence of SEQ ID NO:65; (iii) VH-CDR3 has the amino acid sequenceof SEQ ID NO:66; (iv) VL-CDR1 has the amino acid sequence of SEQ IDNO:71; (v) VL-CDR2 has the amino acid sequence of SEQ ID NO:72; and (vi)VL-CDR3 has the amino acid sequence of SEQ ID NO:73; and wherein theprotein binds ActRIIB; and (h)(i) VH-CDR1 has the amino acid sequence ofSEQ ID NO:78; (ii) VH-CDR2 has the amino acid sequence of SEQ ID NO:79;(iii) VH-CDR3 has the amino acid sequence of SEQ ID NO:80; (iv) VL-CDR1has the amino acid sequence of SEQ ID NO:71; (v) VL-CDR2 has the aminoacid sequence of SEQ ID NO:72; and (vi) VL-CDR3 has the amino acidsequence of SEQ ID NO:73; and wherein the protein binds ActRIIB; (i)(i)VH-CDR1 has the amino acid sequence of SEQ ID NO:3; (ii) VH-CDR2 has theamino acid sequence of SEQ ID NO:4; (iii) VH-CDR3 has the amino acidsequence of SEQ ID NO:46; (iv) VL-CDR1 has the amino acid sequence ofSEQ ID NO:51; (v) VL-CDR2 has the amino acid sequence of SEQ ID NO:52;and (vi) VL-CDR3 has the amino acid sequence of SEQ ID NO:53; andwherein the protein binds ActRIIB; (j)(i) VH-CDR1 has the amino acidsequence of SEQ ID NO:58; (ii) VH-CDR2 has the amino acid sequence ofSEQ ID NO:59; (iii) VH-CDR3 has the amino acid sequence of SEQ ID NO:46;(iv) VL-CDR1 has the amino acid sequence of SEQ ID NO:51; (v) VL-CDR2has the amino acid sequence of SEQ ID NO:52; and (vi) VL-CDR3 has theamino acid sequence of SEQ ID NO:53; and wherein the protein bindsActRIIB; (k)(i) VH-CDR1 has the amino acid sequence of SEQ ID NO:85;(ii) VH-CDR2 has the amino acid sequence of SEQ ID NO:86; (iii) VH-CDR3has the amino acid sequence of SEQ ID NO:87; (iv) VL-CDR1 has the aminoacid sequence of SEQ ID NO:92; (v) VL-CDR2 has the amino acid sequenceof SEQ ID NO:93; and (vi) VL-CDR3 has the amino acid sequence of SEQ IDNO:94; and wherein the protein binds ActRIIB and ActRIIA; (l)(i) VH-CDR1has the amino acid sequence of SEQ ID NO:99; (ii) VH-CDR2 has the aminoacid sequence of SEQ ID NO:100; (iii) VH-CDR3 has the amino acidsequence of SEQ ID NO:101; (iv) VL-CDR1 has the amino acid sequence ofSEQ ID NO:92; (v) VL-CDR2 has the amino acid sequence of SEQ ID NO: 153;and (vi) VL-CDR3 has the amino acid sequence of SEQ ID NO:94; andwherein the protein binds ActRIIB and ActRIIA; (m)(i) VH-CDR1 has theamino acid sequence of SEQ ID NO:106; (ii) VH-CDR2 has the amino acidsequence of SEQ ID NO:107, (iii) VH-CDR3 has the amino acid sequence ofSEQ ID NO 108; (iv) VL-CDR1 has the amino acid sequence of SEQ ID NO:92;(v) VL-CDR2 has the amino acid sequence of SEQ ID NO: 153; and (vi)VL-CDR3 has the amino acid sequence of SEQ ID NO:94; and wherein theprotein binds ActRIIB and ActRIIA; (n)(i) VH-CDR1 has the amino acidsequence of SEQ ID NO:113; (ii) VH-CDR2 has the amino acid sequence ofSEQ ID NO:114; (iii) VH-CDR3 has the amino acid sequence of SEQ IDNO:115; (iv) VL-CDR1 has the amino acid sequence of SEQ ID NO:92; (v)VL-CDR2 has the amino acid sequence of SEQ ID NO: 153; and (vi) VL-CDR3has the amino acid sequence of SEQ ID NO:94; and wherein the proteinbinds ActRIIB and ActRIIA; or (o)(i) VH-CDR1 has the amino acid sequenceof SEQ ID NO:113; (ii) VH-CDR2 has the amino acid sequence of SEQ IDNO:120; (iii) VH-CDR3 has the amino acid sequence of SEQ ID NO:121; (iv)VL-CDR1 has the amino acid sequence of SEQ ID NO:92; (v) VL-CDR2 has theamino acid sequence of SEQ ID NO: 153; and (vi) VL-CDR3 has the aminoacid sequence of SEQ ID NO:94; and wherein the protein binds ActRIIB andActRIIA.

In some aspects an ActRII-binding protein comprises a VH-CDR3 or aVL-CDR3 sequence disclosed herein. In further aspects, theActRII-binding protein comprises a VH-CDR3 or a VL-CDR3 sequencedisclosed in Table 1. In some aspects an ActRII-binding proteincomprises a VH-CDR3 and a VL-CDR3 sequence disclosed herein. In furtheraspects, the ActRII-binding protein comprises a VH-CDR3 and a VL-CDR3sequence disclosed in Table 1.

In further aspects, the disclosure provides an ActRIIB-binding proteincomprising a VH-CDR3 having the amino acid sequence of SEQ ID NO:5, 46,66, or 80. In some aspects, the ActRIIB-binding protein comprises aVH-CDR3 having the amino acid sequence of SEQ ID NO:5. In furtheraspects the ActRIIB-binding protein comprises a VH-CDR3 having the aminoacid sequence of SEQ ID NO:5 and a VH-CDR2 having the amino acidsequence of SEQ ID NO:4, 18, 24, 30, 178, or 36. In further aspects, theActRIIB-binding protein comprises a VH-CDR3 having the amino acidsequence of SEQ ID NO:5, a VH-CDR2 having the amino acid sequence of SEQID NO:4, 18, 24, 30, 178, or 36, and a VH-CDR1 having the amino acidsequence of SEQ ID NO:3, 17, 23, 29, 35, or 41. In some aspects, theActRIIB-binding protein comprises a VH-CDR3 having the amino acidsequence of SEQ ID NO:46. In further aspects the ActRIIB-binding proteincomprises a VH-CDR3 having the amino acid sequence of SEQ ID NO:46 and aVH-CDR2 having the amino acid sequence of SEQ ID NO:4 or 59. In furtheraspects, the ActRIIB-binding protein comprises a VH-CDR3 having theamino acid sequence of SEQ ID NO:46, a VH-CDR2 having the amino acidsequence of SEQ ID NO:4 or 59, and a VH-CDR1 having the amino acidsequence of SEQ ID NO:3 or 58. In some aspects, the ActRIIB-bindingprotein comprises a VH-CDR3 having the amino acid sequence of SEQ IDNO:66. In further aspects the ActRIIB-binding protein comprises aVH-CDR3 having the amino acid sequence of SEQ ID NO:66 and a VH-CDR2having the amino acid sequence of SEQ ID NO:65. In further aspects, theActRIIB-binding protein comprises a VH-CDR3 having the amino acidsequence of SEQ ID NO:66, a VH-CDR2 having the amino acid sequence ofSEQ ID NO:65, and a VH-CDR1 having the amino acid sequence of SEQ IDNO:64. In some aspects, the ActRIIB-binding protein comprises a VH-CDR3having the amino acid sequence of SEQ ID NO:80. In further aspects theActRIIB-binding protein comprises a VH-CDR3 having the amino acidsequence of SEQ ID NO:80 and a VH-CDR2 having the amino acid sequence ofSEQ ID NO:79. In further aspects, the ActRIIB-binding protein comprisesa VH-CDR3 having the amino acid sequence of SEQ ID NO:80, a VH-CDR2having the amino acid sequence of SEQ ID NO:79, and a VH-CDR1 having theamino acid sequence of SEQ ID NO:78. In further aspects, theActRIIB-binding protein has at least one characteristic selected fromthe group consisting of (a) competes with an ActRII ligand (e.g.,activin A, activin B, GDF1, GDF3, GDF8 (myostatin), GDF11, BMP6, BMP7,BMP9, or BMP10) for binding to ActRIIB; (b) decreases thephosphorylation of Smads (e.g., Smad2 and/or Smad3) in cells expressingActRIIB in the presence of an ActRIIB ligand (e.g., activin A or GDF8);(c) decreases the phosphorylation of ALK4 and/or ALK7 in cellsexpressing ActRIIB and ALK4 and/or ALK7 in the presence of an ActRIIBligand; and (d) binds to ActRIIB with a K_(D) of ≤1 nM and ≥1 pM (e.g.,as determined by BIACORE® analysis). In some aspects, theActRIIB-binding protein has 2, 3, or 4 of the above characteristics. Insome aspects, the ActRIIB-binding protein has at least 2 or at least 3of the above characteristics.

In further aspects, the disclosure provides an ActRIIB-binding proteincomprising a VL-CDR3 having the amino acid sequence of SEQ ID NO:12, 53,or 73. In some aspects, the ActRIIB-binding protein comprises a VL-CDR3having the amino acid sequence of SEQ ID NO:12. In further aspects theActRIIB-binding protein comprises a VL-CDR3 having the amino acidsequence of SEQ ID NO:12 and a VL-CDR2 having the amino acid sequence ofSEQ ID NO:11. In further aspects, the ActRIIB-binding protein comprisesa VL-CDR3 having the amino acid sequence of SEQ ID NO:12, a VL-CDR2having the amino acid sequence of SEQ ID NO:11, and a VL-CDR1 having theamino acid sequence of SEQ ID NO:10. In some aspects, theActRIIB-binding protein comprises a VL-CDR3 having the amino acidsequence of SEQ ID NO:53 In further aspects the ActRIIB-binding proteincomprises a VL-CDR3 having the amino acid sequence of SEQ ID NO:53 and aVL-CDR2 having the amino acid sequence of SEQ ID NO:52. In furtheraspects, the ActRIIB-binding protein comprises a VL-CDR3 having theamino acid sequence of SEQ ID NO:53, a VL-CDR2 having the amino acidsequence of SEQ ID NO:52, and a VL-CDR1 having the amino acid sequenceof SEQ ID NO:51. In some aspects, the ActRIIB-binding protein comprisesa VL-CDR3 having the amino acid sequence of SEQ ID NO:73. In furtheraspects the ActRIIB-binding protein comprises a VL-CDR3 having the aminoacid sequence of SEQ ID NO:73 and a VL-CDR2 having the amino acidsequence of SEQ ID NO:72. In further aspects, the ActRIIB-bindingprotein comprises a VL-CDR3 having the amino acid sequence of SEQ IDNO:73, a VL-CDR2 having the amino acid sequence of SEQ ID NO:72, and aVL-CDR1 having the amino acid sequence of SEQ ID NO:71. In furtheraspects, the ActRIIB-binding protein has at least one characteristicselected from the group consisting of (a) competes with an ActRII ligand(e.g., activin A, activin B, GDF1, GDF3, GDF8 (myostatin), GDF11, BMP6,BMP7, BMP9, or BMP10) for binding to ActRIIB; (b) decreases thephosphorylation of Smads (e.g., Smad2 and/or Smad3) in cells expressingActRIIB in the presence of an ActRIIB ligand (e.g., activin A or GDF8);(c) decreases the phosphorylation of ALK4 and/or ALK7 in cellsexpressing ActRIIB and ALK4 and/or ALK7 in the presence of an ActRIIBligand; and (d) binds to ActRIIB with a K_(D) of ≤1 nM and ≥1 pM (e.g.,as determined by BIACORE® analysis). In some aspects, theActRIIB-binding protein has 2, 3, or 4 of the above characteristics. Insome aspects, the ActRIIB-binding protein has at least 2 or at least 3of the above characteristics.

In further aspects, the disclosure provides an ActRIIB- and/orActRIIA-binding protein comprising a VH-CDR3 having the amino acidsequence of SEQ ID NO:87, 101, 108, 115, or 121. In further aspects, theActRII-binding protein comprises a VH-CDR3 having the amino acidsequence of SEQ ID NO:87, 101, 108, 115, or 121, and a VH-CDR2 havingthe amino acid sequence of SEQ ID NO:86, 100, 107, 114, or 120. Infurther aspects, the ActRII-binding protein comprises a VH-CDR3 havingthe amino acid sequence of SEQ ID NO:87, 101, 108, 115, or 121, aVH-CDR2 having the amino acid sequence of SEQ ID NO:86, 100, 107, 114,or 120, and a VH-CDR1 having the amino acid sequence of SEQ ID NO:85,99, 106 or 113. In some aspects, the ActRIIB- and/or ActRIIA bindingprotein comprises a VH-CDR3 having the amino acid sequence of SEQ IDNO:87. In further aspects the ActRIIB- and/or ActRIIA binding proteincomprises a VH-CDR3 having the amino acid sequence of SEQ ID NO:87 and aVH-CDR2 having the amino acid sequence of SEQ ID NO:86. In furtheraspects, the ActRIIB- and/or ActRIIA-binding protein comprises a VH-CDR3having the amino acid sequence of SEQ ID NO:87, a VH-CDR2 having theamino acid sequence of SEQ ID NO:86, and a VH-CDR1 having the amino acidsequence of SEQ ID NO:85. In some aspects, the ActRIIB- and/orActRIIA-binding protein comprises a VH-CDR3 having the amino acidsequence of SEQ ID NO:101. In further aspects the ActRIIB- and/orActRIIA-binding protein comprises a VH-CDR3 having the amino acidsequence of SEQ ID NO:101 and a VH-CDR2 having the amino acid sequenceof SEQ ID NO:100. In further aspects, the ActRIIB- and/orActRIIA-binding protein comprises a VH-CDR3 having the amino acidsequence of SEQ ID NO:101, a VH-CDR2 having the amino acid sequence ofSEQ ID NO:100, and a VH-CDR1 having the amino acid sequence of SEQ IDNO:99. In some aspects, the ActRIIB- and/or ActRIIA-binding proteincomprises a VH-CDR3 having the amino acid sequence of SEQ ID NO:108. Infurther aspects the ActRIIB- and/or ActRIIA-binding protein comprises aVH-CDR3 having the amino acid sequence of SEQ ID NO:108 and a VH-CDR2having the amino acid sequence of SEQ ID NO:107. In further aspects, theActRIIB- and/or ActRIIA-binding protein comprises a VH-CDR3 having theamino acid sequence of SEQ ID NO:108, a VH-CDR2 having the amino acidsequence of SEQ ID NO:107, and a VH-CDR1 having the amino acid sequenceof SEQ ID NO:106. In some aspects, the ActRIIB- and/or ActRIIA-bindingprotein comprises a VH-CDR3 having the amino acid sequence of SEQ IDNO:115. In further aspects the ActRIIB- and/or ActRIIA-binding proteincomprises a VH-CDR3 having the amino acid sequence of SEQ ID NO:115 anda VH-CDR2 having the amino acid sequence of SEQ ID NO:114. In furtheraspects, the ActRIIB- and/or ActRIIA-binding protein comprises a VH-CDR3having the amino acid sequence of SEQ ID NO:115, a VH-CDR2 having theamino acid sequence of SEQ ID NO:114, and a VH-CDR1 having the aminoacid sequence of SEQ ID NO:113. In further aspects, the ActRIIB- and/orActRIIA-binding protein comprises a VH-CDR3 having the amino acidsequence of SEQ ID NO:121, a VH-CDR2 having the amino acid sequence ofSEQ ID NO:120, and a VH-CDR1 having the amino acid sequence of SEQ IDNO:113. In further aspects, the ActRII-binding protein has at least onecharacteristic selected from the group consisting of: (a) competes withan ActRII ligand (e.g., activin A, activin B, GDF1, GDF3, GDF8(myostatin), GDF11, BMP6, BMP7, BMP9, or BMP10) for binding to ActRIIBand/or ActRIIA; (b) decreases the phosphorylation of Smads (e.g., Smad2and/or Smad3) in cells expressing ActRIIB and/or ActRIIA in the presenceof an ActRIIB and/or ActRIIA ligand (e.g., activin A or GDF8); (c)decreases the phosphorylation of ALK4 and/or ALK7 in cells expressingActRIIB and/or ActRIIA and ALK4 and/or ALK7 in the presence of anActRIIB and/or ActRIIA ligand; and (d) binds to ActRIIB and/or ActRIIAwith a K_(D) of ≤1 nM and ≥1 pM (e.g., as determined by BIACORE®analysis). In some aspects, the ActRIIB and/or ActRIIA-binding proteinhas 2, 3, or 4 of the above characteristics. In some aspects, theActRIIB and/or ActRIIA-binding protein has at least 2 or at least 3 ofthe above characteristics.

In further aspects, the disclosure provides an ActRIIB- and/orActRIIA-binding protein comprising a VL-CDR3 having the amino acidsequence of SEQ ID NO:94. In some aspects, the ActRIIB- and/orActRIIA-binding protein comprises a VL-CDR3 having the amino acidsequence of SEQ ID NO:94 and a VL-CDR2 having the amino acid sequence ofSEQ ID NO:93. In further aspects, the ActRIIB-binding protein comprisesa VL-CDR3 having the amino acid sequence of SEQ ID NO:94, a VL-CDR2having the amino acid sequence of SEQ ID NO:93, and a VL-CDR1 having theamino acid sequence of SEQ ID NO:92. In further aspects, theActRII-binding protein has at least one characteristic selected from thegroup consisting of: (a) competes with an ActRII ligand (e.g., activinA, activin B, GDF1, GDF3, GDF8 (myostatin), GDF11, BMP6, BMP7, BMP9, orBMP10) for binding to ActRIIB and/or ActRIIA; (b) decreases thephosphorylation of Smads (e.g., Smad2 and/or Smad3) in cells expressingActRIIB and/or ActRIIA in the presence of an ActRIIB and/or ActRIIAligand (e.g., activin A or GDF8); (c) decreases the phosphorylation ofALK4 and/or ALK7 in cells expressing ActRIIB and/or ActRIIA and ALK4and/or ALK7 in the presence of an ActRIIB and/or ActRIIA ligand; and (d)binds to ActRIIB and/or ActRIIA with a K_(D) of ≤1 nM and ≥1 pM (e.g.,as determined by BIACORE® analysis). In some aspects, the ActRIIB and/orActRIIA-binding protein has 2, 3, or 4 of the above characteristics. Insome aspects, the ActRIIB and/or ActRIIA-binding protein has at least 2or at least 3 of the above characteristics.

In further aspects, the disclosure provides an ActRIIB- and/orActRIIA-binding protein comprising a VH-antigen binding domain 3 (ABD3)having the amino acid sequence of SEQ ID NO:142. In further aspects, theActRII-binding protein comprises a VH-ABD3 having the amino acidsequence of SEQ ID NO:142 and a VH-antigen binding domain 2 (VH-ABD2)having the amino acid sequence of SEQ ID NO:141. In further aspects, theActRII-binding protein comprises a VH-ABD3 having the amino acidsequence of SEQ ID NO:133, a VH-ABD2 having the amino acid sequence ofSEQ ID NO:141, and a VH-antigen binding domain 1 (VH-ABD1) having theamino acid sequence of SEQ ID NO:140. In further aspects, the ActRIIB-and ActRIIA-binding protein has at least one characteristic selectedfrom the group consisting of (a) competes with an ActRII ligand (e.g.,activin A, activin B, GDF1, GDF3, GDF8 (myostatin), GDF11, BMP6, BMP7,BMP9, or BMP10) for binding to ActRIIB or ActRIIA; (b) decreases thephosphorylation of Smads (e.g., Smad2 and/or Smad3) in cells expressingActRIIB and/or ActRIIA in the presence of an ActRIIB and/or ActRIIAligand (e.g., activin A); (c) decreases the phosphorylation of ALK4and/or ALK7 in cells expressing ActRIIB and/or ActRIIA and ALK4 and/orALK7 in the presence of an ActRIIB and/or ActRIIA ligand; and (d) bindsto ActRIIB and/or ActRIIA with a K_(D) of ≤1 nM and ≥1 pM (e.g., asdetermined by BIACORE® analysis). In some aspects, the ActRIIB- andActRIIA-binding protein has 2, 3, or 4 of the above characteristics. Insome aspects, the ActRIIB- and ActRIIA-binding protein has at least 2 orat least 3 of the above characteristics.

In further aspects, the disclosure provides an ActRIIA-binding proteincomprising a VH-CDR3 having the amino acid sequence of SEQ ID NO:128. Infurther aspects, the ActRII-binding protein comprises a VH-CDR3 havingthe amino acid sequence of SEQ ID NO:128 and a VH-CDR2 having the aminoacid sequence of SEQ ID NO:127. In further aspects, the ActRII-bindingprotein comprises a VH-CDR3 having the amino acid sequence of SEQ IDNO:128, a VH-CDR2 having the amino acid sequence of SEQ ID NO:127, and aVH-CDR1 having the amino acid sequence of SEQ ID NO:126. In furtheraspects, the ActRIIA-binding protein has at least one characteristicselected from the group consisting of (a) competes with an ActRIIAligand (e.g., activin A, activin B, GDF1, GDF3, or Nodal); (b) decreasesthe phosphorylation of Smads (e.g., Smad2 and/or Smad3) in cellsexpressing ActRIIA in the presence of an ActRIIA ligand (e.g., activinA); (c) decreases the phosphorylation of ALK4 and/or ALK7 in cellsexpressing ActRIIA and ALK4 and/or ALK7 in the presence of an ActRIIAligand; and (d) binds to ActRIIA with a K_(D) of ≤1 nM and ≥1 pM (e.g.,as determined by BIACORE® analysis). In some aspects, theActRIIA-binding protein has 2, 3, or 4 of the above characteristics. Insome aspects, the ActRIIA-binding protein has at least 2 or at least 3of the above characteristics.

In further aspects, the disclosure provides an ActRIIA-binding proteincomprising a VL-CDR3 having the amino acid sequence of SEQ ID NO:135. Infurther aspects, the ActRII-binding protein comprises a VL-CDR3 havingthe amino acid sequence of SEQ ID NO:135 and a VL-CDR2 having the aminoacid sequence of SEQ ID NO:134. In further aspects, the ActRII-bindingprotein comprises a VL-CDR3 having the amino acid sequence of SEQ IDNO:135, a VL-CDR2 having the amino acid sequence of SEQ ID NO:134, and aVL-CDR1 having the amino acid sequence of SEQ ID NO:133. In furtheraspects, the ActRIIA-binding protein has at least one characteristicselected from the group consisting of (a) competes with an ActRIIAligand (e.g., activin A, activin B, GDF1, GDF3, or Nodal); (b) decreasesthe phosphorylation of Smads (e.g., Smad2 and/or Smad3) in cellsexpressing ActRIIA in the presence of an ActRIIA ligand (e.g., activinA); (c) decreases the phosphorylation of ALK4 and/or ALK7 in cellsexpressing ActRIIA and ALK4 and/or ALK7 in the presence of an ActRIIAligand; and (d) binds to ActRIIA with a K_(D) of ≤1 nM and ≥1 pM (e.g.,as determined by BIACORE® analysis). In some aspects, theActRIIA-binding protein has 2, 3, or 4 of the above characteristics. Insome aspects, the ActRIIA-binding protein has at least 2 or at least 3of the above characteristics.

In some aspects an ActRII-binding protein comprises a VH or a VL whichhas a total of one, two, three, four, five, six, seven, eight, nine,ten, fewer than fifteen, or zero, amino acid substitutions, deletions,and/or insertions compared to a reference VH or VL disclosed herein. Infurther aspects, the ActRII-binding protein comprises a VH or a VL whichhas a total of one, two, three, four, five, six, seven, eight, nine,ten, fewer than fifteen, or zero, amino acid substitutions, deletions,and/or insertions compared to a reference VH or VL disclosed in Table 1.In some aspects an ActRII-binding protein comprises a VH and a VL pairwhich has a total of one, two, three, four, five, six, seven, eight,nine, ten, fewer than fifteen, or zero, amino acid substitutions,deletions, and/or insertions compared to a reference VH and VL pairdisclosed herein. In further aspects, the ActRII-binding proteincomprises a VH and VL pair which has a total of one, two, three, four,five, six, seven, eight, nine, ten, fewer than fifteen, or zero, aminoacid substitutions, deletions, and/or insertions compared to a referenceVH and VL pair disclosed in Table 1.

In some aspects, the ActRII-binding protein comprises a VH and a VL pairselected from the group consisting of: (a)(i) a VH sequence having atotal of one, two, three, four, five, six, seven, eight, nine, ten,fewer than fifteen, or zero, amino acid substitutions, deletions, and/orinsertions from a reference VH sequence selected from the groupconsisting of SEQ ID NO:2, 16, 22, 28, 34, or 40, and (ii) a VL sequencehaving a total of one, two, three, four, five, six, seven, eight, nine,ten, fewer than fifteen, or zero, amino acid substitutions, deletions,and/or insertions from a reference VL sequence of SEQ ID NO:9, andwherein the protein binds ActRIIB; (b)(i) a VH sequence having a totalof one, two, three, four, five, six, seven, eight, nine, ten, fewer thanfifteen, or zero, amino acid substitutions, deletions, and/or insertionsfrom a reference VH sequence of SEQ ID NO:45 or 57, and (ii) a VLsequence having a total of one, two, three, four, five, six, seven,eight, nine, ten, fewer than fifteen, or zero, amino acid substitutions,deletions, and/or insertions from a reference VL sequence of SEQ IDNO:50, and wherein the protein binds ActRIIB; (c)(i) a VH sequencehaving a total of one, two, three, four, five, six, seven, eight, nine,ten, fewer than fifteen, or zero, amino acid substitutions, deletions,and/or insertions from a reference VH sequence of SEQ ID NO:63 or 77,and (ii) a VL sequence having a total of one, two, three, four, five,six, seven, eight, nine, ten, fewer than fifteen, or zero, amino acidsubstitutions, deletions, and/or insertions from a reference VL sequenceof SEQ ID NO:70, and wherein the protein binds ActRIIB; (d)(i) a VHsequence having a total of one, two, three, four, five, six, seven,eight, nine, ten, fewer than fifteen, or zero, amino acid substitutions,deletions, and/or insertions from a reference VH sequence selected fromthe group consisting of SEQ ID NO:84, 98, 105, 112, or 119, and (ii) aVL sequence having a total of one, two, three, four, five, six, seven,eight, nine, ten, fewer than fifteen, or zero, amino acid substitutions,deletions, and/or insertions from a reference VL sequence of SEQ IDNO:91, and wherein the protein binds ActRIIB and ActRIIA; and (e)(i) aVH sequence having a total of one, two, three, four, five, six, seven,eight, nine, ten, fewer than fifteen, or zero, amino acid substitutions,deletions, and/or insertions from a reference VH sequence of SEQ IDNO:125, and (ii) a VL sequence having a total of one, two, three, four,five, six, seven, eight, nine, ten, fewer than fifteen, or zero, aminoacid substitutions, deletions, and/or insertions from a reference VL ofSEQ ID NO:132, and wherein the protein binds ActRIIA.

In some aspects, the ActRII-binding protein comprises a VH and a VL pairhaving (i) a VH sequence having a total of one, two, three, four, five,six, seven, eight, nine, ten, fewer than fifteen, or zero, amino acidsubstitutions, deletions, and/or insertions from a reference VH sequenceof SEQ ID NO:144, and (ii) a VL sequence having a total of one, two,three, four, five, six, seven, eight, nine, ten, fewer than fifteen, orzero, amino acid substitutions, deletions, and/or insertions from areference VL sequence of SEQ ID NO:151, and the protein binds ActRIIB.

In some aspects, the ActRII-binding protein comprises a VH and a VL pairhaving (i) a VH sequence having a total of one, two, three, four, five,six, seven, eight, nine, ten, fewer than fifteen, or zero, amino acidsubstitutions, deletions, and/or insertions from a reference VH sequenceof SEQ ID NO:165, and (ii) a VL sequence having a total of one, two,three, four, five, six, seven, eight, nine, ten, fewer than fifteen, orzero, amino acid substitutions, deletions, and/or insertions from areference VL sequence of SEQ ID NO:172, and the protein binds ActIIRAand ActRIIB.

In a further aspect, the ActRII-binding protein comprises a VH and a VLpair wherein the VH sequence has a total of one, two, three, four, five,six, seven, eight, nine, ten, fewer than fifteen, or zero, amino acidsubstitutions, deletions, and/or insertions from a reference VH sequenceof SEQ ID NO:2; and the VL sequence has a total of one, two, three,four, five, six, seven, eight, nine, ten, fewer than fifteen, or zero,amino acid substitutions, deletions, and/or insertions from a referenceVL sequence of SEQ ID NO:9; and wherein the protein binds ActRIIB; (b)the VH sequence has a total of one, two, three, four, five, six, seven,eight, nine, ten, fewer than fifteen, or zero, amino acid substitutions,deletions, and/or insertions from a reference VH sequence of SEQ IDNO:16; the VL sequence has a total of one, two, three, four, five, six,seven, eight, nine, ten, fewer than fifteen, or zero, amino acidsubstitutions, deletions, and/or insertions from a reference VL sequenceof SEQ ID NO:9; and wherein the protein binds ActRIIB; (c) the VHsequence has a total of one, two, three, four, five, six, seven, eight,nine, ten, fewer than fifteen, or zero, amino acid substitutions,deletions, and/or insertions from a reference VH sequence of SEQ IDNO:22; and the VL sequence has a total of one, two, three, four, five,six, seven, eight, nine, ten, fewer than fifteen, or zero, amino acidsubstitutions, deletions, and/or insertions from a reference VL sequenceof SEQ ID NO:9; and wherein the protein binds ActRIIB; (d) the VHsequence has a total of one, two, three, four, five, six, seven, eight,nine, ten, fewer than fifteen, or zero, amino acid substitutions,deletions, and/or insertions from a reference VH sequence of SEQ IDNO:28; and the VL sequence has a total of one, two, three, four, five,six, seven, eight, nine, ten, fewer than fifteen, or zero, amino acidsubstitutions, deletions, and/or insertions from a reference VL sequenceof SEQ ID NO:9; and wherein the protein binds ActRIIB; (e) the VHsequence has a total of one, two, three, four, five, six, seven, eight,nine, ten, fewer than fifteen, or zero, amino acid substitutions,deletions, and/or insertions from a reference VH sequence of SEQ IDNO:34; and the VL sequence has a total of one, two, three, four, five,six, seven, eight, nine, ten, fewer than fifteen, or zero, amino acidsubstitutions, deletions, and/or insertions from a reference VL sequenceof SEQ ID NO:9; and wherein the protein binds ActRIIB; (f) the VHsequence has a total of one, two, three, four, five, six, seven, eight,nine, ten, fewer than fifteen, or zero, amino acid substitutions,deletions, and/or insertions from a reference VH sequence of SEQ IDNO:40; and the VL sequence has a total of one, two, three, four, five,six, seven, eight, nine, ten, fewer than fifteen, or zero, amino acidsubstitutions, deletions, and/or insertions from a reference VL sequenceof SEQ ID NO:9; and wherein the protein binds ActRIIB; (g) the sequencehas a total of one, two, three, four, five, six, seven, eight, nine,ten, fewer than fifteen, or zero, amino acid substitutions, deletions,and/or insertions from a reference VH sequence of SEQ ID NO:45; and theVL sequence has a total of one, two, three, four, five, six, seven,eight, nine, ten, fewer than fifteen, or zero, amino acid substitutions,deletions, and/or insertions from a reference VL sequence of SEQ IDNO:50; wherein the protein binds ActRIIB; (h) the VH sequence has atotal of one, two, three, four, five, six, seven, eight, nine, ten,fewer than fifteen, or zero, amino acid substitutions, deletions, and/orinsertions from a reference VH sequence of SEQ ID NO:57; and the VLsequence has a total of one, two, three, four, five, six, seven, eight,nine, ten, fewer than fifteen, or zero, amino acid substitutions,deletions, and/or insertions from a reference VL sequence of SEQ IDNO:50; wherein the protein binds ActRIIB; (i) the VH sequence has atotal of one, two, three, four, five, six, seven, eight, nine, ten,fewer than fifteen, or zero, amino acid substitutions, deletions, and/orinsertions from a reference VH sequence of SEQ ID NO:63; and the VLsequence has a total of one, two, three, four, five, six, seven, eight,nine, ten, fewer than fifteen, or zero, amino acid substitutions,deletions, and/or insertions from a reference VL sequence of SEQ IDNO:70; and wherein the protein binds ActRIIB; (j) the VH sequence has atotal of one, two, three, four, five, six, seven, eight, nine, ten,fewer than fifteen, or zero, amino acid substitutions, deletions, and/orinsertions from a reference VH sequence of SEQ ID NO:77; and the VLsequence has a total of one, two, three, four, five, six, seven, eight,nine, ten, fewer than fifteen, or zero, amino acid substitutions,deletions, and/or insertions from a reference VL sequence of SEQ IDNO:70; and wherein the protein binds ActRIIB; (k) the sequence has atotal of one, two, three, four, five, six, seven, eight, nine, ten,fewer than fifteen, or zero, amino acid substitutions, deletions, and/orinsertions from a reference VH sequence of SEQ ID NO:84; and the VLsequence has a total of one, two, three, four, five, six, seven, eight,nine, ten, fewer than fifteen, or zero, amino acid substitutions,deletions, and/or insertions from a reference VL sequence of SEQ IDNO:91; wherein the protein binds ActRIIB and ActRIIA; (l) the VHsequence has a total of one, two, three, four, five, six, seven, eight,nine, ten, fewer than fifteen, or zero, amino acid substitutions,deletions, and/or insertions from a reference VH sequence of SEQ IDNO:98; and the VL sequence has a total of one, two, three, four, five,six, seven, eight, nine, ten, fewer than fifteen, or zero, amino acidsubstitutions, deletions, and/or insertions from a reference VL sequenceof SEQ ID NO:91; wherein the protein binds ActRIIB and ActRIIA; (m) theVH sequence has a total of one, two, three, four, five, six, seven,eight, nine, ten, fewer than fifteen, or zero, amino acid substitutions,deletions, and/or insertions from a reference VH sequence of SEQ IDNO:105; and the VL sequence has a total of one, two, three, four, five,six, seven, eight, nine, ten, fewer than fifteen, or zero, amino acidsubstitutions, deletions, and/or insertions from a reference VL sequenceof SEQ ID NO:91; and wherein the protein binds ActRIIB and ActRIIA; (n)the VH sequence has a total of one, two, three, four, five, six, seven,eight, nine, ten, fewer than fifteen, or zero, amino acid substitutions,deletions, and/or insertions from a reference VH sequence of SEQ IDNO:112; and the VL sequence has a total of one, two, three, four, five,six, seven, eight, nine, ten, fewer than fifteen, or zero, amino acidsubstitutions, deletions, and/or insertions from a reference VL sequenceof SEQ ID NO:91; and wherein the protein binds ActRIIB and ActRIIA; (o)the VH sequence has a total of one, two, three, four, five, six, seven,eight, nine, ten, fewer than fifteen, or zero, amino acid substitutions,deletions, and/or insertions from a reference VH sequence of SEQ IDNO:119; and the VL sequence has a total of one, two, three, four, five,six, seven, eight, nine, ten, fewer than fifteen, or zero, amino acidsubstitutions, deletions, and/or insertions from a reference VL sequenceof SEQ ID NO:91; and wherein the protein binds ActRIIB and ActRIIA; or(p) the VH sequence has a total of one, two, three, four, five, six,seven, eight, nine, ten, fewer than fifteen, or zero, amino acidsubstitutions, deletions, and/or insertions from a reference VH sequenceof SEQ ID NO:125; and the VL sequence has a total of one, two, three,four, five, six, seven, eight, nine, ten, fewer than fifteen, or zero,amino acid substitutions, deletions, and/or insertions from a referenceVL sequence of SEQ ID NO:132; and wherein the protein binds ActRIIA.

In a further aspect, the ActRII-binding protein comprises a VH and a VLpair wherein the VH sequence has a total of one, two, three, four, five,six, seven, eight, nine, ten, fewer than fifteen, or zero, amino acidsubstitutions, deletions, and/or insertions from a reference VH sequenceof SEQ ID NO:144; and the VL sequence has a total of one, two, three,four, five, six, seven, eight, nine, ten, fewer than fifteen, or zero,amino acid substitutions, deletions, and/or insertions from a referenceVL sequence of SEQ ID NO:151, and wherein the protein binds ActRIIB.

In a further aspect, the ActRII-binding protein comprises a VH and a VLpair wherein the VH sequence has a total of one, two, three, four, five,six, seven, eight, nine, ten, fewer than fifteen, or zero, amino acidsubstitutions, deletions, and/or insertions from a reference VH sequenceof SEQ ID NO:165; and the VL sequence has a total of one, two, three,four, five, six, seven, eight, nine, ten, fewer than fifteen, or zero,amino acid substitutions, deletions, and/or insertions from a referenceVL sequence of SEQ ID NO:172, and wherein the protein binds ActIIRA andActRIIB.

In some aspects an ActRII-binding protein comprises a VH or a VL whichhas at least 90%, 95%, 97%, 98%, or 99% sequence identity to a referenceVH or VL disclosed herein. In further aspects, the ActRII-bindingprotein comprises a VH or a VL which has at least 90%, 95%, 97%, 98%, or99% sequence identity to a reference VH or VL disclosed in Table 1. Insome aspects an ActRII-binding protein comprises a VH and VL which hasat least 90%, 95%, 97%, 98%, or 99% sequence identity to a reference VHand VL disclosed herein. In further aspects, the ActRII-binding proteincomprises a VH and VL which has at least 90%, 95%, 97%, 98%, or 99%sequence identity to a reference VH and VL disclosed in Table 1. Infurther aspects, the ActRIIB-binding protein has at least onecharacteristic selected from the group consisting of: (a) competes withan ActRII ligand (e.g., activin A, activin B, GDF1, GDF3, GDF8(myostatin), GDF11, BMP6, BMP7, BMP9, or BMP10) for binding to ActRII;(b) decreases the phosphorylation of Smads (e.g., Smad2 and/or Smad3) incells expressing ActRII in the presence of an ActRII ligand (e.g.,activin A or GDF8); (c) decreases the phosphorylation of ALK4 and/orALK7 in cells expressing ActRII and ALK4 and/or ALK7 in the presence ofan ActRII ligand; and (d) binds to ActRII with a K_(D) of ≤1 nM and ≥1pM (e.g., as determined by BIACORE® analysis). In some aspects, theActRII-binding protein has 2, 3, or 4 of the above characteristics. Insome aspects, the ActRII-binding protein has at least 2 or at least 3 ofthe above characteristics.

In some aspects, the ActRII-binding protein specifically binds ActRIIand comprises a VH and a VL pair selected from the group consisting of:(a)(i) a VH having at least 90%, 95%, 97%, 98%, or 99% sequence identityto SEQ ID NO:2, 16, 22, 28, 34, or 40, and (ii) a VL having at least90%, 95%, 97%, 98%, or 99% sequence identity to SEQ ID NO:9, and whereinthe protein binds ActRIIB; (b)(i) a VH having at least 90%, 95%, 97%,98%, or 99% sequence identity to SEQ ID NO:45 or 57, and (ii) a VLhaving at least 90%, 95%, 97%, 98%, or 99% sequence identity to SEQ IDNO:50, and wherein the protein binds ActRIIB; (c)(i) a VH having atleast 90%, 95%, 97%, 98%, or 99% sequence identity to SEQ ID NO:63 or77, and (ii) a VL having at least 90%, 95%, 97%, 98%, or 99% sequenceidentity to SEQ ID NO:70, and wherein the protein binds ActRIIB; (d)(i)a VH having the amino acid sequence of SEQ ID NO:84, 98, 105, 112, or119, and (ii) a VL having the amino acid sequence of SEQ ID NO:91, andwherein the protein binds ActRIIB and ActRIIA; and (e)(i) a VH having atleast 90%, 95%, 97%, 98%, or 99% sequence identity to SEQ ID NO:125, and(ii) a VL having at least 90%, 95%, 97%, 98%, or 99% sequence identityto SEQ ID NO:132, and wherein the protein binds ActRIIA. In furtheraspects, the ActRIIB-binding protein has at least one characteristicselected from the group consisting of: (a) competes with an ActRIIligand (e.g., activin A, activin B, GDF1, GDF3, GDF8 (myostatin), GDF11,BMP6, BMP7, BMP9, or BMP10) for binding to ActRII; (b) decreases thephosphorylation of Smads (e.g., Smad2 and/or Smad3) in cells expressingActRII in the presence of an ActRII ligand (e.g., activin A or GDF8);(c) decreases the phosphorylation of ALK4 and/or ALK7 in cellsexpressing ActRII and ALK4 and/or ALK7 in the presence of an ActRIIligand; and (d) binds to ActRII with a K_(D) of ≤1 nM and ≥1 pM (e.g.,as determined by BIACORE® analysis). In some aspects, the ActRII-bindingprotein has 2, 3, or 4 of the above characteristics. In some aspects,the ActRII-binding protein has at least 2 or at least 3 of the abovecharacteristics.

In some aspects, the ActRII-binding protein binds ActRIIB and comprisesa VH and VL pair selected from (i) a VH having at least 90%, 95%, 97%,98%, or 99% sequence identity to SEQ ID NO:144, and (ii) a VL having atleast 90%, 95%, 97%, 98%, or 99% sequence identity to SEQ ID NO:151, andthe protein binds ActRIIB. In further aspects, the ActRIIB-bindingprotein has at least one characteristic selected from the groupconsisting of: (a) competes with an ActRII ligand (e.g., activin A,activin B, GDF1, GDF3, GDF8 (myostatin), GDF11, BMP6, BMP7, BMP9, orBMP10) for binding to ActRII; (b) decreases the phosphorylation of Smads(e.g., Smad2 and/or Smad3) in cells expressing ActRII in the presence ofan ActRII ligand (e.g., activin A or GDF8); (c) decreases thephosphorylation of ALK4 and/or ALK7 in cells expressing ActRII and ALK4and/or ALK7 in the presence of an ActRII ligand; and (d) binds to ActRIIwith a K_(D) of ≤1 nM and ≥1 pM (e.g., as determined by BIACORE®analysis). In some aspects, the ActRII-binding protein has 2, 3, or 4 ofthe above characteristics. In some aspects, the ActRII-binding proteinhas at least 2 or at least 3 of the above characteristics.

In some aspects, the ActRII-binding protein binds ActRIIB and comprisesa VH having at least 90%, 95%, 97%, 98%, or 99% sequence identity to SEQID NO:165, and (ii) a VL having at least 90%, 95%, 97%, 98%, or 99%sequence identity to SEQ ID NO:172, and the protein binds ActIIRA andActRIIB. In further aspects, the ActRII-binding protein has at least onecharacteristic selected from the group consisting of: (a) competes withan ActRII ligand (e.g., activin A, activin B, GDF1, GDF3, GDF8(myostatin), GDF11, BMP6, BMP7, BMP9, or BMP10) for binding to ActRII;(b) decreases the phosphorylation of Smads (e.g., Smad2 and/or Smad3) incells expressing ActRII in the presence of an ActRII ligand (e.g.,activin A or GDF8); (c) decreases the phosphorylation of ALK4 and/orALK7 in cells expressing ActRII and ALK4 and/or ALK7 in the presence ofan ActRII ligand; and (d) binds to ActRII with a K_(D) of ≤1 nM and ≥1pM (e.g., as determined by BIACORE® analysis). In some aspects, theActRII-binding protein has 2, 3, or 4 of the above characteristics. Insome aspects, the ActRII-binding protein has at least 2 or at least 3 ofthe above characteristics.

In a further aspect, the ActRII-binding protein specifically bindsActRII and comprises a VH and a VL pair selected from the groupconsisting of: (a) a VH sequence of SEQ ID NO:2, 16, 22, 28, 34, or 40,and a VL sequence of SEQ ID NO:9; and wherein the protein binds ActRIIB;(b) a VH sequence of SEQ ID NO:45 or 57, and a VL sequence of SEQ IDNO:50; and wherein the protein binds ActRIIB; (c) a VH sequence of SEQID NO:63 or 77, and a VL sequence of SEQ ID NO:70; and wherein theprotein binds ActRIIB; (d) a VH sequence of SEQ ID NO:84, 98, 105, 112,or 119, and a VL sequence of SEQ ID NO:91; and wherein the protein bindsActRIIB; and (e) a VH sequence of SEQ ID NO:125, and a VL sequence ofSEQ ID NO:132 and wherein the protein binds ActRIIA. In a furtheraspect, the ActRII-binding protein comprises a VH and a VL pair selectedfrom the group consisting of: (a) a VH sequence of SEQ ID NO:2 and a VLsequence of SEQ ID NO:9; (b) a VH sequence of SEQ ID NO:16 and a VLsequence of SEQ ID NO:9; (c) a VH sequence of SEQ ID NO:22 and a VLsequence of SEQ ID NO:9; (d) a VH sequence of SEQ ID NO:28 and a VLsequence of SEQ ID NO:9; (e) a VH sequence of SEQ ID NO:34 and a VLsequence of SEQ ID NO:9; (f) a VH sequence of SEQ ID NO:40 and a VLsequence of SEQ ID NO:9; (g) a VH sequence of SEQ ID NO:45 and a VLsequence of SEQ ID NO:50; (h) a VH sequence of SEQ ID NO:57 and a VLsequence of SEQ ID NO:50; (i) a VH sequence of SEQ ID NO:63 and a VLsequence of SEQ ID NO:70; (j) a VH sequence of SEQ ID NO:77 and a VLsequence of SEQ ID NO:70; (k) a VH sequence of SEQ ID NO:84 and a VLsequence of SEQ ID NO:91; (l) a VH sequence of SEQ ID NO:98 and a VLsequence of SEQ ID NO:91; (m) a VH sequence of SEQ ID NO:105 and a VLsequence of SEQ ID NO:91; (n) a VH sequence of SEQ ID NO:112 and a VLsequence of SEQ ID NO:91; (o) VH sequence of SEQ ID NO:119 and a VLsequence of SEQ ID NO:91; and (p) VH sequence of SEQ ID NO:125 and a VLsequence of SEQ ID NO:132.

In a further aspect, the ActRII-binding protein specifically bindsActRII and comprises a VH sequence of SEQ ID NO:144 and a VL sequence ofSEQ ID NO:151, and the protein binds ActRIIB.

In a further aspect, the ActRII-binding protein specifically bindsActRII and comprises a VH sequence of SEQ ID NO:165 and a VL sequence ofSEQ ID NO:172, and the protein binds ActIIRA and ActRIIB.

In some aspects, the ActRII-binding protein comprises a VH and VL pairselected from the group consisting of: (a) a VH having at least 90%,95%, 97%, 98%, or 99% sequence identity to SEQ ID NO:2 and a VL havingat least 90%, 95%, 97%, 98%, or 99% sequence identity to SEQ ID NO:9 andwherein the protein binds ActRIIB; (b) a VH having at least 90%, 95%,97%, 98%, or 99% sequence identity to SEQ ID NO:16 and a VL having atleast 90%, 95%, 97%, 98%, or 99% sequence identity to SEQ ID NO:9 andwherein the protein binds ActRIIB; (c) a VH having at least 90%, 95%,97%, 98%, or 99% sequence identity to SEQ ID NO:22 and a VL having atleast 90%, 95%, 97%, 98%, or 99% sequence identity to SEQ ID NO:9, andwherein the protein binds ActRIIB; (d) a VH having at least 90%, 95%,97%, 98%, or 99% sequence identity to SEQ ID NO:28 and a VL having atleast 90%, 95%, 97%, 98%, or 99% sequence identity to SEQ ID NO:9, andwherein the protein binds ActRIIB; (e) a VH having at least 90%, 95%,97%, 98%, or 99% sequence identity to SEQ ID NO:34 and a VL having atleast 90%, 95%, 97%, 98%, or 99% sequence identity to SEQ ID NO:9, andwherein the protein binds ActRIIB; (f) a VH having at least 90%, 95%,97%, 98%, or 99% sequence identity to SEQ ID NO:40 and a VL having atleast 90%, 95%, 97%, 98%, or 99% sequence identity to SEQ ID NO:9, andwherein the protein binds ActRIIB; (g) a VH having at least 90%, 95%,97%, 98%, or 99% sequence identity to SEQ ID NO:45 and a VL having atleast 90%, 95%, 97%, 98%, or 99% sequence identity to SEQ ID NO:50, andwherein the protein binds ActRIIB; (h) a VH having at least 90%, 95%,97%, 98%, or 99% sequence identity to SEQ ID NO:57 and a VL having atleast 90%, 95%, 97%, 98%, or 99% sequence identity to SEQ ID NO:50,wherein the protein binds ActRIIB; (i) a VH having at least 90%, 95%,97%, 98%, or 99% sequence identity to SEQ ID NO:63 and a VL having atleast 90%, 95%, 97%, 98%, or 99% sequence identity to SEQ ID NO:70, andwherein the protein binds ActRIIB; (j) a VH having at least 90%, 95%,97%, 98%, or 99% sequence identity to SEQ ID NO:77 and a VL having atleast 90%, 95%, 97%, 98%, or 99% sequence identity to SEQ ID NO:70; andwherein the protein binds ActRIIB; (k) a VH having at least 90%, 95%,97%, 98%, or 99% sequence identity to SEQ ID NO:84 and a VL having atleast 90%, 95%, 97%, 98%, or 99% sequence identity to SEQ ID NO:91, andwherein the protein binds ActRIIB and ActRIIA; (l) a VH having at least90%, 95%, 97%, 98%, or 99% sequence identity to SEQ ID NO:98 and a VHhaving at least 90%, 95%, 97%, 98%, or 99% sequence identity to SEQ IDNO:91, and wherein the protein binds ActRIIB and ActRIIA; (m) a VHhaving at least 90%, 95%, 97%, 98%, or 99% sequence identity to SEQ IDNO:105 and a VL having at least 90%, 95%, 97%, 98%, or 99% sequenceidentity to SEQ ID NO:91, and wherein the protein binds ActRIIB andActRIIA; (n) a VH having at least 90%, 95%, 97%, 98%, or 99% sequenceidentity to SEQ ID NO:112 and a VL having at least 90%, 95%, 97%, 98%,or 99% sequence identity to SEQ ID NO:91, and wherein the protein bindsActRIIB and ActRIIA; (o) a VH having at least 90%, 95%, 97%, 98%, or 99%sequence identity to SEQ ID NO:119 and a VL having at least 90%, 95%,97%, 98%, or 99% sequence identity to SEQ ID NO:91, and wherein theprotein binds ActRIIB and ActRIIA; and (p) a VH having at least 90%,95%, 97%, 98%, or 99% sequence identity to SEQ ID NO:125 and a VL havingat least 90%, 95%, 97%, 98%, or 99% sequence identity to SEQ ID NO:132,and wherein the protein binds ActRIIA. In further aspects, theActRIIB-binding protein has at least one characteristic selected fromthe group consisting of: (a) competes with an ActRII ligand (e.g.,activin A, activin B, GDF1, GDF3, GDF8 (myostatin), GDF11, BMP6, BMP7,BMP9, or BMP10) for binding to ActRII; (b) decreases the phosphorylationof Smads (e.g., Smad2 and/or Smad3) in cells expressing ActRII in thepresence of an ActRII ligand (e.g., activin A or GDF8); (c) decreasesthe phosphorylation of ALK4 and/or ALK7 in cells expressing ActRII andALK4 and/or ALK7 in the presence of an ActRII ligand; and (d) binds toActRII with a K_(D) of ≤1 nM and ≥1 pM (e.g., as determined by BIACORE®analysis). In some aspects, the ActRII-binding protein has 2, 3, or 4 ofthe above characteristics. In some aspects, the ActRII-binding proteinhas at least 2 or at least 3 of the above characteristics.

In some aspects, the ActRII-binding protein comprises a VH having atleast 90%, 95%, 97%, 98%, or 99% sequence identity to SEQ ID NO:144 anda VL having at least 90%, 95%, 97%, 98%, or 99% sequence identity to SEQID NO:151; and the protein binds ActRIIB. In further aspects, theActRIIB-binding protein has at least one characteristic selected fromthe group consisting of: (a) competes with an ActRII ligand (e.g.,activin A, activin B, GDF1, GDF3, GDF8 (myostatin), GDF11, BMP6, BMP7,BMP9, or BMP10) for binding to ActRII; (b) decreases the phosphorylationof Smads (e.g., Smad2 and/or Smad3) in cells expressing ActRII in thepresence of an ActRII ligand (e.g., activin A or GDF8); (c) decreasesthe phosphorylation of ALK4 and/or ALK7 in cells expressing ActRII andALK4 and/or ALK7 in the presence of an ActRII ligand; and (d) binds toActRII with a K_(D) of ≤1 nM and ≥1 pM (e.g., as determined by BIACORE®analysis). In some aspects, the ActRII-binding protein has 2, 3, or 4 ofthe above characteristics. In some aspects, the ActRII-binding proteinhas at least 2 or at least 3 of the above characteristics.

In some aspects, the ActRII-binding protein comprises a VH having atleast 90%, 95%, 97%, 98%, or 99% sequence identity to SEQ ID NO:165 anda VL having at least 90%, 95%, 97%, 98%, or 99% sequence identity to SEQID NO:172; and the protein binds ActIIRA and ActRIIB. In furtheraspects, the ActRII-binding protein has at least one characteristicselected from the group consisting of: (a) competes with an ActRIIligand (e.g., activin A, activin B, GDF1, GDF3, GDF8 (myostatin), GDF11,BMP6, BMP7, BMP9, or BMP10) for binding to ActRII; (b) decreases thephosphorylation of Smads (e.g., Smad2 and/or Smad3) in cells expressingActRII in the presence of an ActRII ligand (e.g., activin A or GDF8);(c) decreases the phosphorylation of ALK4 and/or ALK7 in cellsexpressing ActRII and ALK4 and/or ALK7 in the presence of an ActRIIligand; and (d) binds to ActRII with a K_(D) of ≤1 nM and ≥1 pM (e.g.,as determined by BIACORE® analysis). In some aspects, the ActRII-bindingprotein has 2, 3, or 4 of the above characteristics. In some aspects,the ActRII-binding protein has at least 2 or at least 3 of the abovecharacteristics.

In some aspects, the ActRII-binding protein comprises a VH and VL pairselected from the group consisting of: (a) a VH sequence of SEQ ID NO:2and a VL sequence of SEQ ID NO:9; (b) a VH sequence of SEQ ID NO:16 anda VL sequence of SEQ ID NO:9; (c) a VH sequence of SEQ ID NO:22 and a VLsequence of SEQ ID NO:9; (d) a VH sequence of SEQ ID NO:28 and a VLsequence of SEQ ID NO:9 (e) a VH sequence of SEQ ID NO:34 and a VLsequence of SEQ ID NO:9; (f) a VH sequence of SEQ ID NO:40 and a VLsequence of SEQ ID NO:9; (g) a VH sequence of SEQ ID NO:45 and a VLsequence of SEQ ID NO:50; (h) a VH sequence of SEQ ID NO:57 and a VLsequence of SEQ ID NO:50; (i) a VH sequence of SEQ ID NO:63 and a VLsequence of SEQ ID NO:70; (j) a VH sequence of SEQ ID NO:77 and a VLsequence of SEQ ID NO:70; (k) a VH sequence of SEQ ID NO:84 and a VLsequence of SEQ ID NO:91; (l) a VH sequence of SEQ ID NO:98 and a VLsequence of SEQ ID NO:91; (m) a VH sequence of SEQ ID NO:105 and a VLsequence of SEQ ID NO:91; (n) a VH sequence of SEQ ID NO:112 and a VLsequence of SEQ ID NO:91; (o) VH sequence of SEQ ID NO:119 and asequence of SEQ ID NO:91; and (p) VH sequence of SEQ ID NO:125 and asequence of SEQ ID NO:132.

In some aspects, the ActRII-binding protein comprises a VH sequence ofSEQ ID NO:144 and a VL sequence of SEQ ID NO:151.

In some aspects, the ActRII-binding protein comprises a VH sequence ofSEQ ID NO:165 and a VL sequence of SEQ ID NO:172.

In some aspects, the ActRII-binding protein specifically binds ActRIIBand comprises a VH having at least 90%, 95%, 97%, 98%, or 99% sequenceidentity to SEQ ID NO:2, 16, 22, 28, 34, 40, 45, 57, 63, or 77. In someaspects, the ActRII-binding protein comprises a VH having at least 90%,95%, 97%, 98%, or 99% sequence identity to SEQ ID NO:2. In some aspects,the ActRII-binding protein comprises a VH having at least 90%, 95%, 97%,98%, or 99% sequence identity to SEQ ID NO:16. In some aspects, theActRII-binding protein comprises a VH having at least 90%, 95%, 97%,98%, or 99% sequence identity to SEQ ID NO: 22. In some aspects, theActRII-binding protein comprises a VH having at least 90%, 95%, 97%,98%, or 99% sequence identity to SEQ ID NO: 28. In some aspects, theActRII-binding protein comprises a VH having at least 90%, 95%, 97%,98%, or 99% sequence identity to SEQ ID NO: 34. In some aspects, theActRII-binding protein comprises a VH having at least 90%, 95%, 97%,98%, or 99% sequence identity to SEQ ID NO: 40. In some aspects, theActRII-binding protein comprises a VH having at least 90%, 95%, 97%,98%, or 99% sequence identity to SEQ ID NO: 45. In some aspects, theActRII-binding protein comprises a VH having at least 90%, 95%, 97%,98%, or 99% sequence identity to SEQ ID NO: 57. In some aspects, theActRII-binding protein comprises a VH having at least 90%, 95%, 97%,98%, or 99% sequence identity to SEQ ID NO:63. In some aspects, theActRII-binding protein comprises a VH having at least 90%, 95%, 97%,98%, or 99% sequence identity to SEQ ID NO:77. In some aspects, theActRII-binding protein specifically binds ActRIIB and comprises a VLhaving at least 90%, 95%, 97%, 98%, or 99% sequence identity to SEQ IDNO:9, 50, or 70. In further aspects, the ActRII-binding proteinspecifically binds ActRIIB and comprises a VH having at least 90%, 95%,97%, 98%, or 99% sequence identity to SEQ ID NO:2, 16, 22, 28, 34, or40, and a VL having at least 90%, 95%, 97%, 98%, or 99% sequenceidentity to SEQ ID NO:9. In further aspects, the ActRII-binding proteinspecifically binds ActRIIB and comprises a VH having at least 90%, 95%,97%, 98%, or 99% sequence identity to SEQ ID NO: 45 or 57. In someaspects, the ActRII-binding protein specifically binds ActRIIB andcomprises a VL having at least 90%, 95%, 97%, 98%, or 99% sequenceidentity to SEQ ID NO:50. In further aspects, the ActRII-binding proteinspecifically binds ActRIIB and comprises a VH having at least 90%, 95%,97%, 98%, or 99% sequence identity to SEQ ID NO: 45 or 57, and a VLhaving at least 90%, 95%, 97%, 98%, or 99% sequence identity to SEQ IDNO:50. In some aspects, the ActRII-binding protein specifically bindsActRIIB and comprises a VH and a VL, wherein, the VH has at least 90%,95%, 97%, 98%, or 99% sequence identity to SEQ ID NO: 63 or 77; and theVL has at least 90%, 95%, 97%, 98%, or 99% sequence identity to SEQ IDNO:70. In further aspects, the ActRII-binding protein specifically bindsActRIIB and comprises a VH having at least 90%, 95%, 97%, 98%, or 99%sequence identity to SEQ ID NO: 63 or 77, and a VL having at least 90%,95%, 97%, 98%, or 99% sequence identity to SEQ ID NO:70. In furtheraspects, the ActRIIB-binding protein has at least one characteristicselected from the group consisting of (a) competes with an ActRII ligand(e.g., activin A, activin B, GDF1, GDF3, GDF8 (myostatin), GDF11, BMP6,BMP7, BMP9, or BMP10) for binding to ActRIIB; (b) decreases thephosphorylation of Smads (e.g., Smad2 and/or Smad3) in cells expressingActRIIB in the presence of an ActRIIB ligand (e.g., activin A or GDF8);(c) decreases the phosphorylation of ALK4 and/or ALK7 in cellsexpressing ActRIIB and ALK4 and/or ALK7 in the presence of an ActRIIBligand; and (d) binds to ActRIIB with a K_(D) of ≤1 nM and ≥1 pM (e.g.,as determined by BIACORE® analysis). In some aspects, theActRIIB-binding protein has 2, 3, or 4 of the above characteristics. Insome aspects, the ActRIIB-binding protein has at least 2 or at least 3of the above characteristics.

In some aspects, the ActRII-binding protein specifically binds ActRIIBand comprises a VH having at least 90%, 95%, 97%, 98%, or 99% sequenceidentity to SEQ ID NO:144. In some aspects, the ActRII-binding proteinspecifically binds ActRIIB and comprises a VL having at least 90%, 95%,97%, 98%, or 99% sequence identity to SEQ ID NO:151. In some aspects,the ActRII-binding protein specifically binds ActRIIB and comprises a VHand a VL, wherein, the VH has at least 90%, 95%, 97%, 98%, or 99%sequence identity to SEQ ID NO:144; and the VL has at least 90%, 95%,97%, 98%, or 99% sequence identity to SEQ ID NO:151. In further aspects,the ActRII-binding protein specifically binds ActRIIB and comprises a VHhaving the amino acid sequence of SEQ ID NO:144 and a VL having theamino acid sequence of SEQ ID NO:151. In further aspects, theActRIIB-binding protein has at least one characteristic selected fromthe group consisting of (a) competes with an ActRII ligand (e.g.,activin A, activin B, GDF1, GDF3, GDF8 (myostatin), GDF11, BMP6, BMP7,BMP9, or BMP10) for binding to ActRIIB; (b) decreases thephosphorylation of Smads (e.g., Smad2 and/or Smad3) in cells expressingActRIIB in the presence of an ActRIIB ligand (e.g., activin A or GDF8);(c) decreases the phosphorylation of ALK4 and/or ALK7 in cellsexpressing ActRIIB and ALK4 and/or ALK7 in the presence of an ActRIIBligand; and (d) binds to ActRIIB with a K_(D) of ≤1 nM and ≥1 pM (e.g.,as determined by BIACORE® analysis). In some aspects, theActRIIB-binding protein has 2, 3, or 4 of the above characteristics. Insome aspects, the ActRIIB-binding protein has at least 2 or at least 3of the above characteristics.

In some aspects, the ActRII-binding protein specifically binds ActIIRAand ActRIIB and comprises a VH having at least 90%, 95%, 97%, 98%, or99% sequence identity to SEQ ID NO:165. In some aspects, theActRII-binding protein specifically binds ActIIRA and ActRIIB andcomprises a VL having at least 90%, 95%, 97%, 98%, or 99% sequenceidentity to SEQ ID NO:172. In some aspects, the ActRII-binding proteinspecifically binds ActIIRA and ActRIIB and comprises a VH and a VL,wherein, the VH has at least 90%, 95%, 97%, 98%, or 99% sequenceidentity to SEQ ID NO:165; and the VL has at least 90%, 95%, 97%, 98%,or 99% sequence identity to SEQ ID NO:172. In further aspects, theActRII-binding protein specifically binds ActIIRA and ActRIIB andcomprises a VH having the amino acid sequence of SEQ ID NO:165 and a VLhaving the amino acid sequence of SEQ ID NO:172. In further aspects, theActRII-binding protein has at least one characteristic selected from thegroup consisting of (a) competes with an ActRII ligand (e.g., activin A,activin B, GDF1, GDF3, GDF8 (myostatin), GDF11, BMP6, BMP7, BMP9, orBMP10) for binding to ActRIIA and/or ActRIIB; (b) decreases thephosphorylation of Smads (e.g., Smad2 and/or Smad3) in cells expressingActRIIA and/or ActRIIB in the presence of an ActRIIA and/or ActRIIBligand (e.g., activin A or GDF8); (c) decreases the phosphorylation ofALK4 and/or ALK7 in cells expressing ActRIIA and/or ActRIIB and ALK4and/or ALK7 in the presence of an ActRIIA and/or ActRIIB ligand; and (d)binds to each of ActRIIA and ActRIIB with a K_(D) of ≤1 nM and ≥1 pM(e.g., as determined by BIACORE® analysis). In some aspects, theActRII-binding protein has 2, 3, or 4 of the above characteristics. Insome aspects, the ActRII-binding protein has at least 2 or at least 3 ofthe above characteristics.

In some aspects, the ActRII-binding protein specifically binds ActRIIBand ActRIIA and comprises a VH having at least 90%, 95%, 97%, 98%, or99% sequence identity to SEQ ID NO: SEQ ID NO:84, 98, 105, 112, or 119.In some aspects, the ActRII-binding protein specifically binds ActRIIBand ActRIIA and comprises a VH having at least 90%, 95%, 97%, 98%, or99% sequence identity to SEQ ID NO:84. In some aspects, theActRII-binding protein specifically binds ActRIIB and ActRIIA andcomprises a VH having at least 90%, 95%, 97%, 98%, or 99% sequenceidentity to SEQ ID NO: SEQ ID NO: 98. In some aspects, theActRII-binding protein specifically binds ActRIIB and ActRIIA andcomprises a VH having at least 90%, 95%, 97%, 98%, or 99% sequenceidentity to SEQ ID NO: SEQ ID NO:105. In some aspects, theActRII-binding protein specifically binds ActRIIB and ActRIIA andcomprises a VH having at least 90%, 95%, 97%, 98%, or 99% sequenceidentity to SEQ ID NO: SEQ ID NO:112. In some aspects, theActRII-binding protein specifically binds ActRIIB and ActRIIA andcomprises a VH having at least 90%, 95%, 97%, 98%, or 99% sequenceidentity to SEQ ID NO: SEQ ID NO:119. In some aspects, theActRII-binding protein specifically binds ActRIIB and ActRIIA andcomprises a VL having at least 90%, 95%, 97%, 98%, or 99% sequenceidentity to SEQ ID NO:91. In further aspects, the ActRII-binding proteinspecifically binds ActRIIB and ActRIIA and comprises a VH having atleast 90%, 95%, 97%, 98%, or 99% sequence identity to SEQ ID NO:84, 98,105, 112, or 119, and a VL having at least 90%, 95%, 97%, 98%, or 99%sequence identity to SEQ ID NO:91. In further aspects, theActRII-binding protein specifically binds ActRIIB and ActRIIA andcomprises a VH having at least 90%, 95%, 97%, 98%, or 99% sequenceidentity to SEQ ID NO:84, and a VL having at least 90%, 95%, 97%, 98%,or 99% sequence identity to SEQ ID NO:91. In further aspects, theActRII-binding protein specifically binds ActRIIB and ActRIIA andcomprises a VH having at least 90%, 95%, 97%, 98%, or 99% sequenceidentity to SEQ ID NO: 98 and a VL having at least 90%, 95%, 97%, 98%,or 99% sequence identity to SEQ ID NO:91. In further aspects, theActRII-binding protein specifically binds ActRIIB and ActRIIA andcomprises a VH having at least 90%, 95%, 97%, 98%, or 99% sequenceidentity to SEQ ID NO:105 and a VL having at least 90%, 95%, 97%, 98%,or 99% sequence identity to SEQ ID NO:91. In further aspects, theActRII-binding protein specifically binds ActRIIB and/or ActRIIA andcomprises a VH having at least 90%, 95%, 97%, 98%, or 99% sequenceidentity to SEQ ID NO: 112 and a VL having at least 90%, 95%, 97%, 98%,or 99% sequence identity to SEQ ID NO:91. In further aspects, theActRII-binding protein specifically binds ActRIIB and ActRIIA andcomprises a VH having at least 90%, 95%, 97%, 98%, or 99% sequenceidentity to SEQ ID NO:119, and a VL having at least 90%, 95%, 97%, 98%,or 99% sequence identity to SEQ ID NO:91. In further aspects, theActRIIB- and ActRIIA-binding protein has at least one characteristicselected from the group consisting of: (a) competes with an ActRIIligand (e.g., activin A, activin B, GDF1, GDF3, GDF8 (myostatin), GDF11,BMP6, BMP7, BMP9, or BMP10) for binding to ActRIIB and ActRIIA; (b)decreases the phosphorylation of Smads (e.g., Smad2 and/or Smad3) incells expressing ActRIIB and/or ActRIIA in the presence of an ActRIIBand/or ActRIIA ligand (e.g., activin A or GDF8); (c) decreases thephosphorylation of ALK4 and/or ALK7 in cells expressing ActRIIB and/orActRIIA and ALK4 and/or ALK7 in the presence of an ActRIIB and/orActRIIA ligand; and (d) binds to ActRIIB and/or ActRIIA with a K_(D) of≤1 nM and ≥1 pM (e.g., as determined by BIACORE® analysis). In someaspects, the ActRIIB and ActRIIA-binding protein has 2, 3, or 4 of theabove characteristics. In some aspects, the ActRIIB and ActRIIA-bindingprotein has at least 2 or at least 3 of the above characteristics.

In some aspects, the ActRII-binding protein specifically binds ActRIIAand comprises a VH having at least 90%, 95%, 97%, 98%, or 99% sequenceidentity to SEQ ID NO:125. In some aspects, the ActRII-binding proteinspecifically binds ActRIIA and comprises a VL having at least 90%, 95%,97%, 98%, or 99% sequence identity to SEQ ID NO:132. In some aspects,the ActRII-binding protein specifically binds ActRIIA and comprises a VHand a VL, wherein, the VH has at least 90%, 95%, 97%, 98%, or 99%sequence identity to SEQ ID NO:125; and the VL has at least 90%, 95%,97%, 98%, or 99% sequence identity to SEQ ID NO:132. In further aspects,the ActRIIA-binding protein has at least one characteristic selectedfrom the group consisting of (a) competes with an ActRIIA ligand (e.g.,activin A, activin B, GDF1, GDF3, or Nodal); (b) decreases thephosphorylation of Smads (e.g., Smad2 and/or Smad3) in cells expressingActRIIA in the presence of an ActRIIA ligand (e.g., activin A); (c)decreases the phosphorylation of ALK4 and/or ALK7 in cells expressingActRIIA and ALK4 and/or ALK7 in the presence of an ActRIIA ligand; and(d) binds to ActRIIA with a K_(D) of ≤1 nM and ≥1 pM (e.g., asdetermined by BIACORE® analysis). In some aspects, the ActRIIA-bindingprotein has 2, 3, or 4 of the above characteristics. In some aspects,the ActRIIA-binding protein has at least 2 or at least 3 of the abovecharacteristics.

In additional aspects an ActRII-binding protein competes for binding toActRII with an antibody comprising a VH and a VL sequence pair disclosedherein. In additional aspects an ActRII-binding protein competes forbinding to ActRII with an antibody comprising a VH and a VL sequencepair disclosed in Table 1. In certain aspects, an ActRII-binding proteinbinds to the same epitope as an ActRII-binding protein disclosed herein.In additional aspects, an ActRII-binding protein binds to the sameepitope as an ActRII-binding protein disclosed in Table 1. The abilityof an ActRII-binding protein to compete for binding with and/or bind thesame epitope of ActRII as a reference ActRII-binding protein can readilybe determined using techniques disclosed herein or otherwise known inthe art.

In some aspects, the ActRII-binding protein specifically binds ActRIIBand comprises a VH of SEQ ID NO:2, 16, 22, 28, 34, 40, 45, 57, 63, or77. In additional aspects, the ActRII-binding protein specifically bindsActRIIB and comprises a VL of SEQ ID NO:9, 50, or 70. In furtheraspects, the ActRII-binding protein specifically binds ActRIIB andcomprises a VH of SEQ ID NO:2, 16, 22, 28, 34, 40, 45, 57, 63, or 77;and a VL of SEQ ID NO:9, 50, or 70. In some aspects, the ActRII-bindingprotein specifically binds ActRIIB and comprises a VH of SEQ ID NO:144.In additional aspects, the ActRII-binding protein specifically bindsActRIIB and comprises a VL of SEQ ID NO:151. In further aspects, theActRII-binding protein specifically binds ActRIIB and comprises a VH ofSEQ ID NO:144 and a VL of SEQ ID NO:151. In further aspects, theActRII-binding protein specifically binds ActRIIB but does notspecifically bind ActRIIA. In some aspects, the ActRII-binding proteinspecifically binds ActRIIA and ActRIIB and comprises a VH of SEQ IDNO:165. In additional aspects, the ActRII-binding protein specificallybinds ActRIIA and ActRIIB and comprises a VL of SEQ ID NO:172. Infurther aspects, the ActRII-binding protein specifically binds ActRIIAand ActRIIB and comprises a VH of SEQ ID NO:165 and a VL of SEQ IDNO:172. In further aspects, the ActRII-binding protein specificallybinds ActRIIA and ActRIIB.

In some aspects, the ActRII-binding protein binds amino acid residuesNANWELERT (SEQ ID NO:157) of ActRIIB. In some aspects, theActRII-binding protein binds amino acid residues NANWELERT (SEQ IDNO:157) of ActRIIB, but does not bind AcRIIA. In some aspects, theActRII-binding protein binds amino acid residues VKKGCWLDD (SEQ IDNO:158) of ActRIIB, but does not bind AcRIIA. In some aspects, theActRII-binding protein binds amino acid residues NANWELERT (SEQ IDNO:157) and amino acid residues VKKGCWLDD (SEQ ID NO:158) of ActRIIB. Infurther aspects, the ActRII-binding protein binds amino acid residuesNANWELERT (SEQ ID NO:157) and amino acid residues VKKGCWLDD (SEQ IDNO:158) of ActRIIB, but does not bind ActRIIA.

In some aspects, the ActRII-binding protein binds a polypeptide selectedfrom the group consisting of: (a) amino acid residues NANWELERT (SEQ IDNO:157) of ActRIIB; (b) amino acid residues CCEGNFCNER (SEQ ID NO:159)of ActRIIB; (c) amino acid residues CCEGNMCNEK (SEQ ID NO:161) ofActRIIA; and (d) amino acid residues ECLFFNANWEKD (SEQ ID NO:162) ofActRIIA.

In some aspects, the ActRII-binding protein binds a polypeptide or a setof polypeptides selected from the group consisting of: (a) amino acidresidues NANWELERT (SEQ ID NO:157) and amino acid residues CCEGNFCNER(SEQ ID NO:159) of ActRIIB; (b) amino acid residues NANWELERT (SEQ IDNO:157) and amino acid residues VKKGCWLDD (SEQ ID NO:158) of ActRIIB;(c) amino acid residues NANWELERT (SEQ ID NO:157), amino acid residuesCCEGNFCNER (SEQ ID NO:159), and amino acid residues GCWLDDFNCYDR (SEQ IDNO:160) of ActRIIB; (d) amino acid residues NANWELERT (SEQ ID NO:157) ofActRIIB and amino acid residues ECLFFNANWEKD (SEQ ID NO:162) of ActRIIA;(e) amino acid residues NANWELERT (SEQ ID NO:157), amino acid residuesGCWLDDFNCYDR (SEQ ID NO:160), and amino acid residues VKKGCWLDD (SEQ IDNO:158) of ActRIIB; (f) amino acid residues CCEGNFCNER (SEQ ID NO:159)of ActRIIB and amino acid residues CCEGNMCNEK (SEQ ID NO:161) ofActRIIA; (g) amino acid residues CCEGNMCNEK (SEQ ID NO:161), amino acidresidues ECLFFNANWEKD (SEQ ID NO:162), and amino acid residues CWLDDINCYDRT (SEQ ID NO:163) of ActRIIA; (h) amino acid residues NANWELERT(SEQ ID NO:157), amino acid residues CCEGNFCNER (SEQ ID NO:159), andamino acid residues GCWLDDFNCYDR (SEQ ID NO:160) of ActRIIB, and aminoacid residues CCEG NMCNEK (SEQ ID NO:161), amino acid residuesECLFFNANWEKD (SEQ ID NO:162), and amino acid residues CWLDDINCYDRT (SEQID NO:163) of ActRIIA.

In some aspects, the ActRII-binding protein competes for binding toActRIIB with an antibody comprising a VH of SEQ ID NO:2, 16, 22, 28, 34,40, 45, 57, 63, 77, or 144, and a VL of SEQ ID NO:9, 50, 70, or 151. Infurther aspects, the ActRII-binding protein binds the same epitope ofActRIIB and/or ActRIIA as an antibody comprising a VH of SEQ ID NO:2,16, 22, 28, 34, 40, 45, 57, 63, 77, or 144, and a VL of SEQ ID NO:9, 50,70, or 151.

In some aspects, the ActRIIB-binding protein (e.g., an anti-ActRIIBantibody) comprises a VH of SEQ ID NO:2 and a VL of SEQ ID NO:9. In someaspects, an ActRIIB-binding protein competes for binding to ActRIIB withan antibody comprising a VH of SEQ ID NO:2 and a VL of SEQ ID NO:9. Infurther aspects, the ActRII-binding protein binds the same epitope ofActRIIB as an antibody comprising a VH of SEQ ID NO:2 and a VL of SEQ IDNO:9.

In some aspects, the ActRIIB-binding protein comprises a VH of SEQ IDNO:16 and a VL of SEQ ID NO:9. In some aspects, an ActRIIB-bindingprotein competes for binding to ActRIIB with an antibody comprising a VHof SEQ ID NO:16 and a VL of SEQ ID NO:9. In further aspects, theActRII-binding protein binds the same epitope of ActRIIB as an antibodycomprising a VH of SEQ ID NO:16 and a VL of SEQ ID NO:9.

In some aspects, the ActRIIB-binding protein comprises a VH of SEQ IDNO:22 and a VL of SEQ ID NO:9. In some aspects, an ActRIIB-bindingprotein competes for binding to ActRIIB with an antibody comprising a VHof SEQ ID NO:22 and a VL of SEQ ID NO:9. In further aspects, theActRII-binding protein binds the same epitope of ActRIIB as an antibodycomprising a VH of SEQ ID NO:22 and a VL of SEQ ID NO:9.

In some aspects, the ActRIIB-binding protein comprises a VH of SEQ IDNO:28 and a VL of SEQ ID NO:9. In some aspects, an ActRIIB-bindingprotein competes for binding to ActRIIB with an antibody comprising a VHof SEQ ID NO:28 and a VL of SEQ ID NO:9. In further aspects, theActRII-binding protein binds the same epitope of ActRIIB as an antibodycomprising a VH of SEQ ID NO:28 and a VL of SEQ ID NO:9.

In some aspects, the ActRIIB-binding protein comprises a VH of SEQ IDNO:34 and a VL of SEQ ID NO:9. In some aspects, an ActRIIB-bindingprotein competes for binding to ActRIIB with an antibody comprising a VHof SEQ ID NO:34 and a VL of SEQ ID NO:9. In further aspects, theActRII-binding protein binds the same epitope of ActRIIB as an antibodycomprising a VH of SEQ ID NO:34 and a VL of SEQ ID NO:9.

In some aspects, the ActRIIB-binding protein comprises a VH of SEQ IDNO:40 and a VL of SEQ ID NO:9. In some aspects, an ActRIIB-bindingprotein competes for binding to ActRIIB with an antibody comprising a VHof SEQ ID NO:40 and a VL of SEQ ID NO:9. In further aspects, theActRII-binding protein binds the same epitope of ActRIIB as an antibodycomprising a VH of SEQ ID NO:40 and a VL of SEQ ID NO:9.

In some aspects, the ActRIIB-binding protein comprises a VH of SEQ IDNO:45 and a VL of SEQ ID NO:50. In some aspects, an ActRIIB-bindingprotein competes for binding to ActRIIB with an antibody comprising a VHof SEQ ID NO:45 and a VL of SEQ ID NO:50. In further aspects, theActRII-binding protein binds the same epitope of ActRIIB as an antibodycomprising a VH of SEQ ID NO:45 and a VL of SEQ ID NO:50.

In some aspects, the ActRIIB-binding protein comprises a VH of SEQ IDNO:57 and a VL of SEQ ID NO:50. In some aspects, an ActRIIB-bindingprotein competes for binding to ActRIIB with an antibody comprising a VHof SEQ ID NO:57 and a VL of SEQ ID NO:50. In further aspects, theActRII-binding protein binds the same epitope of ActRIIB as an antibodycomprising a VH of SEQ ID NO:57 and a VL of SEQ ID NO:50.

In some aspects, the ActRIIB-binding protein comprises a VH of SEQ IDNO:63 and a VL of SEQ ID NO:70. In some aspects, an ActRIIB-bindingprotein competes for binding to ActRIIB with an antibody comprising a VHof SEQ ID NO:63 and a VL of SEQ ID NO:70. In further aspects, theActRII-binding protein binds the same epitope of ActRIIB as an antibodycomprising a VH of SEQ ID NO:63 and a VL of SEQ ID NO:70.

In some aspects, the ActRIIB-binding protein comprises a VH of SEQ IDNO:77 and a VL of SEQ ID NO:70. In some aspects, an ActRIIB-bindingprotein competes for binding to ActRIIB with an antibody comprising a VHof SEQ ID NO:77 and a VL of SEQ ID NO:70. In further aspects, theActRII-binding protein binds the same epitope of ActRIIB as an antibodycomprising a VH of SEQ ID NO:77 and a VL of SEQ ID NO:70.

In some aspects, the ActRIIB-binding protein comprises a VH of SEQ IDNO:144 and a VL of SEQ ID NO:151. In some aspects, an ActRIIB-bindingprotein competes for binding to ActRIIB with an antibody comprising a VHof SEQ ID NO:144 and a VL of SEQ ID NO:151. In further aspects, theActRII-binding protein binds the same epitope of ActRIIB as an antibodycomprising a VH of SEQ ID NO:144 and a VL of SEQ ID NO:151.

In some aspects, the ActRII-binding protein comprises a VH of SEQ IDNO:165 and a VL of SEQ ID NO:172. In some aspects, an ActRIIB-bindingprotein competes for binding to ActRIIB with an antibody comprising a VHof SEQ ID NO:165 and a VL of SEQ ID NO:172. In further aspects, theActRII-binding protein binds the same epitope of ActRIIB as an antibodycomprising a VH of SEQ ID NO:165 and a VL of SEQ ID NO:172.

In some aspects, the ActRII-binding protein comprises a VH of SEQ IDNO:165 and a VL of SEQ ID NO:172. In some aspects, an ActRIIA-bindingprotein competes for binding to ActRIIA with an antibody comprising a VHof SEQ ID NO:165 and a VL of SEQ ID NO:172. In further aspects, theActRII-binding protein binds the same epitope of ActRIIA as an antibodycomprising a VH of SEQ ID NO:165 and a VL of SEQ ID NO:172.

In some aspects, the ActRIIB-binding protein competes for binding toamino acid residues NANWELERT (SEQ ID NO:157) of ActRIIB with anantibody comprising a VH of SEQ ID NO:144 and a VL of SEQ ID NO:151. Insome aspects, the ActRIIB-binding protein competes for binding to aminoacid residues VKKGCWLDD (SEQ ID NO:158) of ActRIIB with an antibodycomprising a VH of SEQ ID NO:144 and a VL of SEQ ID NO:151. In someaspects, the ActRIIB-binding protein competes for binding to amino acidresidues NANWELERT (SEQ ID NO:157) and amino acid residues VKKGCWLDD(SEQ ID NO:158) of ActRIIB, with an antibody comprising a VH of SEQ IDNO:144 and a VL of SEQ ID NO:151. In further aspects, theActRIIB-binding protein does not specifically bind ActRIIA.

In some aspects, the ActRII-binding protein competes for binding toActRIIB and/or ActRIIA with an antibody comprising a VH of SEQ ID NO:84,98, 105, 112, or 119 and a VL of SEQ ID NO:91. In further aspects, theActRII-binding protein binds the same epitope of ActRIIB and/or ActRIIAas an antibody comprising a VH of SEQ ID NO:84, 98, 105, 112, or 119;and a VL of SEQ ID NO:91.

In some aspects, the ActRII-binding protein binds amino acid residuesCCEGNFCNER (SEQ ID NO:159) of ActRIIB.

In some aspects, the ActRII-binding protein binds amino acid residuesGCWLDDFNCYDR (SEQ ID NO:160) of ActRIIB.

In some aspects, the ActRII-binding protein binds amino acid residuesNANWELERT (SEQ ID NO:157) of ActRIIB. In some aspects, theActRII-binding protein binds amino acid residues NANWELERT (SEQ IDNO:157) and amino acid residues GCWLDDFNCYDR (SEQ ID NO:160) of ActRIIB.In some embodiments, the ActRII-binding protein binds amino acidresidues NANWELERT (SEQ ID NO:157) and amino acid residues CCEGNFCNER(SEQ ID NO:159) of ActRIIB. In further embodiments, the ActRII-bindingprotein binds amino acid residues NANWELERT (SEQ ID NO:157), amino acidresidues CCEGNFCNER (SEQ ID NO:159), and amino acid residuesGCWLDDFNCYDR (SEQ ID NO:160) of ActRIIB.

In some aspects, the ActRII-binding protein binds amino acid residuesCCEGNMCNEK (SEQ ID NO:161) of ActRIIA.

In some aspects, the ActRII-binding protein binds amino acid residuesECLFFNANWEKD (SEQ ID NO:162) of ActRIIA. In further aspects, theActRII-binding protein binds amino acid residues CCEGNMCNEK (SEQ IDNO:161) and amino acid residues ECLFFNANWEKD (SEQ ID NO:162) of ActRIIA.

In some aspects, the ActRII-binding protein binds amino acid residuesCWLDDINCYDRT (SEQ ID NO:163) of ActRIIA. In further embodiments, theActRII-binding protein binds amino acid residues CCEGNMCNEK (SEQ IDNO:161), amino acid residues ECLFFNANWEKD (SEQ ID NO:162), and aminoacid residues CWLDDINCYDRT (SEQ ID NO:163) of ActRIIA.

In some aspects, the ActRII-binding protein binds amino acid residuesCCEGNFCNER (SEQ ID NO:159) of ActRIIB and amino acid residues CCEGNMCNEK(SEQ ID NO:161) of ActRIIA.

In some aspects, the ActRII-binding protein binds amino acid residuesNANWELERT (SEQ ID NO:157) of ActRIIB and amino acid residuesECLFFNANWEKD (SEQ ID NO:162) of ActRIIA. In further aspects, theActRII-binding protein binds amino acid residues CCEGNFCNER (SEQ IDNO:159) and amino acid residues NANWELERT (SEQ ID NO:157) of ActRIIB andamino acid residues CCEGNMCNEK (SEQ ID NO:161) and amino acid residuesECLFFNANWEKD (SEQ ID NO:162) of ActRIIA. In further aspects, theActRII-binding protein binds amino acid residues CCEGNFCNER (SEQ IDNO:159), amino acid residues NANWELERT (SEQ ID NO:157) and amino acidresidues GCWLDDFNCYDR (SEQ ID NO:160) of ActRIIB and amino acid residuesCCEGNMCNEK (SEQ ID NO:161), amino acid residues ECLFFNANWEKD (SEQ IDNO:162), and amino acid residues CWLDDINCYDRT (SEQ ID NO:163) ofActRIIA.

In some aspects, the ActRIIB- and ActRIIA-binding protein comprises a VHof SEQ ID NO:84 and a VL of SEQ ID NO:91. In some aspects, anActRIIB-binding protein competes for binding to ActRIIB and ActRIIA withan antibody comprising a VH of SEQ ID NO:84 and a VL of SEQ ID NO:91. Infurther aspects, the ActRII-binding protein binds the same epitope ofActRIIB and ActRIIA as an antibody comprising a VH of SEQ ID NO:84 and aVL of SEQ ID NO:91.

In some aspects, the ActRIIB- and ActRIIA-binding protein comprises a VHof SEQ ID NO:165 and a VL of SEQ ID NO:172. In some aspects, anActRIIB-binding protein competes for binding to ActRIIB and ActRIIA withan antibody comprising a VH of SEQ ID NO:165 and a VL of SEQ ID NO:172.In further aspects, the ActRII-binding protein binds the same epitope ofActRIIB and ActRIIA as an antibody comprising a VH of SEQ ID NO:165 anda VL of SEQ ID NO:172.

In some aspects, the ActRIIB- and ActRIIA-binding protein competes forbinding to amino acid residues CCEGNFCNER (SEQ ID NO:159) of ActRIIBwith an antibody comprising a VH of SEQ ID NO:84 and a VL of SEQ IDNO:91. In some aspects, the ActRIIB and ActRIIA-binding protein competesfor binding to amino acid residues NANWELERT (SEQ ID NO:157) of ActRIIBwith an antibody comprising a VH of SEQ ID NO:84 and a VL of SEQ IDNO:91. In further aspects, the ActRIIB- and ActRIIA-binding proteincompetes for binding to amino acid residues CCEGNFCNER (SEQ ID NO:159)and amino acid residues NANWELERT (SEQ ID NO:157) of ActRIIB with anantibody comprising a VH of SEQ ID NO:84 and a VL of SEQ ID NO:91.

In some aspects, the ActRIIB- and ActRIIA-binding protein competes forbinding to amino acid residues CCEGNFCNER (SEQ ID NO:159) of ActRIIBwith an antibody comprising a VH of SEQ ID NO:165 and a VL of SEQ IDNO:172. In some aspects, the ActRIIB and ActRIIA-binding proteincompetes for binding to amino acid residues NANWELERT (SEQ ID NO:157) ofActRIIB with an antibody comprising a VH of SEQ ID NO:165 and a VL ofSEQ ID NO:172. In further aspects, the ActRIIB- and ActRIIA-bindingprotein competes for binding to amino acid residues CCEGNFCNER (SEQ IDNO:159) and amino acid residues NANWELERT (SEQ ID NO:157) of ActRIIBwith an antibody comprising a VH of SEQ ID NO:165 and a VL of SEQ IDNO:172.

In some aspects, the ActRIIB- and ActRIIA-binding protein competes forbinding to amino acid residues GCWLDDFNCYDR (SEQ ID NO:160) of ActRIIBwith an antibody comprising a VH of SEQ ID NO:84 and a VL of SEQ IDNO:91.

In some aspects, the ActRIIB- and ActRIIA-binding protein competes forbinding to amino acid residues GCWLDDFNCYDR (SEQ ID NO:160) of ActRIIBwith an antibody comprising a VH of SEQ ID NO:165 and a VL of SEQ IDNO:172.

In some aspects, the ActRIIB- and ActRIIA-binding protein competes forbinding to amino acid residues CCEGNFCNER (SEQ ID NO:159), amino acidresidues NANWELERT (SEQ ID NO:157), and amino acid residues GCWLDDFNCYDR(SEQ ID NO:160) of ActRIIB with an antibody comprising a VH of SEQ IDNO:84 and a VL of SEQ ID NO:91.

In some aspects, the ActRIIB- and ActRIIA-binding protein competes forbinding to amino acid residues CCEGNFCNER (SEQ ID NO:159), amino acidresidues NANWELERT (SEQ ID NO:157), and amino acid residues GCWLDDFNCYDR(SEQ ID NO:160) of ActRIIB with an antibody comprising a VH of SEQ IDNO:165 and a VL of SEQ ID NO:172.

In some aspects, the ActRII-binding protein specifically binds ActRIIBand ActRIIA and comprises a VH of SEQ ID NO:84, 98, 105, 112, or 119. Inadditional aspects, the ActRII-binding protein specifically bindsActRIIB and ActRIIA and comprises a VL of SEQ ID NO:91. In furtheraspects, the ActRII-binding protein specifically binds ActRIIB andActRIIA and comprises a VH of SEQ ID NO:84, 98, 105, 112, or 119; and aVL of SEQ ID NO:91.

In some aspects, the ActRII-binding protein specifically binds ActRIIBand ActRIIA and comprises a VH of SEQ ID NO:165. In additional aspects,the ActRII-binding protein specifically binds ActRIIB and ActRIIA andcomprises a VL of SEQ ID NO:172. In further aspects, the ActRII-bindingprotein specifically binds ActRIIB and ActRIIA and comprises a VH of SEQID NO:165; and a VL of SEQ ID NO:172.

In some aspects, the ActRIIB- and ActRIIA-binding protein comprises a VHof SEQ ID NO:84 and a VL of SEQ ID NO:91. In further aspects, theActRII-binding protein binds the same epitope of ActRIIB and ActRIIA asan antibody comprising a VH of SEQ ID NO:84 and a VL of SEQ ID NO:91.

In some aspects, the ActRIIB- and ActRIIA-binding protein comprises a VHof SEQ ID NO:98 and a VL of SEQ ID NO:91. In some aspects, anActRIIB-binding protein competes for binding to ActRIIB and ActRIIA withan antibody comprising a VH of SEQ ID NO:98 and a VL of SEQ ID NO:91. Infurther aspects, the ActRII-binding protein binds the same epitope ofActRIIB and ActRIIA as an antibody comprising a VH of SEQ ID NO:98 and aVL of SEQ ID NO:91.

In some aspects, the ActRIIB- and ActRIIA-binding protein comprises a VHof SEQ ID NO:105 and a VL of SEQ ID NO:91. In some aspects, anActRIIB-binding protein competes for binding to ActRIIB and ActRIIA withan antibody comprising a VH of SEQ ID NO:105 and a VL of SEQ ID NO:91.In further aspects, the ActRII-binding protein binds the same epitope ofActRIIB and ActRIIA as an antibody comprising a VH of SEQ ID NO:105 anda VL of SEQ ID NO:91.

In some aspects, the ActRIIB- and ActRIIA-binding protein comprises a VHof SEQ ID NO:112 and a VL of SEQ ID NO:91. In some aspects, anActRIIB-binding protein competes for binding to ActRIIB and ActRIIA withan antibody comprising a VH of SEQ ID NO:112 and a VL of SEQ ID NO:91.In further aspects, the ActRII-binding protein binds the same epitope ofActRIIB and ActRIIA as an antibody comprising a VH of SEQ ID NO:112 anda VL of SEQ ID NO:91.

In some aspects, the ActRIIB- and ActRIIA-binding protein comprises a VHof SEQ ID NO:119 and a VL of SEQ ID NO:91. In some aspects, anActRIIB-binding protein competes for binding to ActRIIB and ActRIIA withan antibody comprising a VH of SEQ ID NO:119 and a VL of SEQ ID NO:91.In further aspects, the ActRII-binding protein binds the same epitope ofActRIIB and ActRIIA as an antibody comprising a VH of SEQ ID NO:119 anda VL of SEQ ID NO:91.

In some aspects, the ActRIIA-binding protein comprises a VH of SEQ IDNO:125 and a VL of SEQ ID NO:132. In some aspects, an ActRIIA-bindingprotein competes for binding to ActRIIA with an antibody comprising a VHof SEQ ID NO:125 and a VL of SEQ ID NO:132. In further aspects, theActRII-binding protein binds the same epitope of ActRIIA as an antibodycomprising a VH of SEQ ID NO:125 and a VL of SEQ ID NO:132.

In some aspects, the ActRII-binding protein specifically binds ActRIIBand comprises a set of CDRs: VH-CDR1, VH-CDR2, and VH-CDR3, wherein theset of CDRs is identical to, or has a total of one, two, three, four,five, six, seven, eight, nine, ten, or fewer than ten, amino acidsubstitutions, deletions, and/or insertions from a reference set of CDRsin which: (a) VH-CDR1 has the amino acid sequence of SEQ ID NO:3 or 58;(b) VH-CDR2 has the amino acid sequence of SEQ ID NO:4 or 59; or (c)VH-CDR3 has the amino acid sequence of SEQ ID NO:46. In further aspects,the ActRIIB-binding protein has at least one characteristic selectedfrom the group consisting of (a) competes with an ActRII ligand (e.g.,activin A, activin B, GDF1, GDF3, GDF8 (myostatin), GDF11, BMP6, BMP7,BMP9, or BMP10) for binding to ActRIIB; (b) decreases thephosphorylation of Smads (e.g., Smad2 and/or Smad3) in cells expressingActRIIB in the presence of an ActRIIB ligand (e.g., activin A or GDF8);(c) decreases the phosphorylation of ALK4 and/or ALK7 in cellsexpressing ActRIIB and ALK4 and/or ALK7 in the presence of an ActRIIBligand; and (d) binds to ActRIIB with a K_(D) of ≤1 nM and ≥1 pM (e.g.,as determined by BIACORE® analysis). In some aspects, theActRIIB-binding protein has 2, 3, or 4 of the above characteristics. Insome aspects, the ActRIIB-binding protein has at least 2 or at least 3of the above characteristics.

In some aspects, the ActRII-binding protein specifically binds ActRIIBand comprises a set of CDRs: VL-CDR1, VL-CDR2, and VL-CDR3, wherein theset of CDRs is identical to, or has a total of one, two, three, four,five, six, seven, eight, nine, ten, or fewer than ten, amino acidsubstitutions, deletions, and/or insertions from a reference set of CDRsin which: (a) VL-CDR1 has the amino acid sequence of SEQ ID NO:51; (b)VL-CDR2 has the amino acid sequence of SEQ ID NO:52; or (c) VL-CDR3 hasthe amino acid sequence of SEQ ID NO:53. In further aspects, theActRIIB-binding protein has at least one characteristic selected fromthe group consisting of (a) competes with an ActRII ligand (e.g.,activin A, activin B, GDF1, GDF3, GDF8 (myostatin), GDF11, BMP6, BMP7,BMP9, or BMP10) for binding to ActRIIB; (b) decreases thephosphorylation of Smads (e.g., Smad2 and/or Smad3) in cells expressingActRIIB in the presence of an ActRIIB ligand (e.g., activin A or GDF8);(c) decreases the phosphorylation of ALK4 and/or ALK7 in cellsexpressing ActRIIB and ALK4 and/or ALK7 in the presence of an ActRIIBligand; and (d) binds to ActRIIB with a K_(D) of ≤1 nM and ≥1 pM (e.g.,as determined by BIACORE® analysis). In some aspects, theActRIIB-binding protein has 2, 3, or 4 of the above characteristics. Insome aspects, the ActRIIB-binding protein has at least 2 or at least 3of the above characteristics.

In additional aspects, the ActRII-binding protein specifically bindsActRIIB and comprises a set of CDRs: VH-CDR1, VH-CDR2, VH-CDR3, VL-CDR1,VL-CDR2, and VL-CDR3, wherein the set of CDRs is identical to, or has atotal of one, two, three, four, five, six, seven, eight, nine, ten, orfewer than ten, amino acid substitutions, deletions, and/or insertionsfrom a reference set of CDRs in which: (a) VH-CDR1 has the amino acidsequence of SEQ ID NO:3 or 58; (b) VH-CDR2 has the amino acid sequenceof SEQ ID NO:4 or 59; (c) VH-CDR3 has the amino acid sequence of SEQ IDNO:46; (d) VL-CDR1 has the amino acid sequence of SEQ ID NO:51; (e)VL-CDR2 has the amino acid sequence of SEQ ID NO:52; or (f) VL-CDR3 hasthe amino acid sequence of SEQ ID NO:53. In further aspects, theActRIIB-binding protein has at least one characteristic selected fromthe group consisting of (a) competes with an ActRII ligand (e.g.,activin A, activin B, GDF1, GDF3, GDF8 (myostatin), GDF11, BMP6, BMP7,BMP9, or BMP10) for binding to ActRIIB; (b) decreases thephosphorylation of Smads (e.g., Smad2 and/or Smad3) in cells expressingActRIIB in the presence of an ActRIIB ligand (e.g., activin A or GDF8);(c) decreases the phosphorylation of ALK4 and/or ALK7 in cellsexpressing ActRIIB and ALK4 and/or ALK7 in the presence of an ActRIIBligand; and (d) binds to ActRIIB with a K_(D) of ≤1 nM and ≥1 pM (e.g.,as determined by BIACORE® analysis). In some aspects, theActRIIB-binding protein has 2, 3, or 4 of the above characteristics. Insome aspects, the ActRIIB-binding protein has at least 2 or at least 3of the above characteristics.

In further aspects, the ActRII-binding protein specifically bindsActRIIB and ActRIIA and comprises a set of VH antigen binding domains(ABDs): VH-ABD1, VH-ABD2, VH-ABD3, VL-ABD1, VL-ABD2, and VL-ABD3,wherein: (a) VH-ABD1 has the amino acid sequence of SEQ ID NO:140; (b)VH-ABD2 has the amino acid sequence of SEQ ID NO:141; (c) VH-ABD3 hasthe amino acid sequence of SEQ ID NO:142; (d) VL-ABD1 has the amino acidsequence of SEQ ID NO:92; (e) VL-ABD2 has the amino acid sequence of SEQID NO:93; or (f) VL-ABD3 has the amino acid sequence of SEQ ID NO:94. Infurther aspects, the ActRIIB-binding protein comprises a VH and a VL. Infurther aspects, the ActRIIB- and ActRIIA-binding protein has at leastone characteristic selected from the group consisting of (a) competeswith an ActRII ligand (e.g., activin A, activin B, GDF1, GDF3, GDF8(myostatin), GDF11, BMP6, BMP7, BMP9, or BMP10) for binding to ActRIIBor ActRIIA; (b) decreases the phosphorylation of Smads (e.g., Smad2and/or Smad3) in cells expressing ActRIIB and/or ActRIIA in the presenceof an ActRIIB and/or ActRIIA ligand (e.g., activin A); (c) decreases thephosphorylation of ALK4 and/or ALK7 in cells expressing ActRIIB and/orActRIIA and ALK4 and/or ALK7 in the presence of an ActRIIB and/orActRIIA ligand; and (d) binds to ActRIIB and/or ActRIIA with a K_(D) of≤1 nM and ≥1 pM (e.g., as determined by BIACORE® analysis). In someaspects, the ActRIIB- and ActRIIA-binding protein has 2, 3, or 4 of theabove characteristics. In some aspects, the ActRIIB- and ActRIIA-bindingprotein has at least 2 or at least 3 of the above characteristics.

In some aspects, the ActRII-binding protein specifically binds ActRIIAand comprises a VH and a VL wherein the VH sequence is identical to, orhas a total of one, two, three, four, five, six, seven, eight, nine,ten, fewer than fifteen, or zero, amino acid substitutions, deletions,and/or insertions from a reference VH sequence of SEQ ID NO:125, andwherein the VL sequence is identical to, or has a total of one, two,three, four, five, six, seven, eight, nine, ten, fewer than fifteen, orzero, amino acid substitutions, additions and/or deletions from areference VL sequence of SEQ ID NO:132. In further aspects, theActRIIA-binding protein has at least one characteristic selected fromthe group consisting of (a) competes with an ActRIIA ligand (e.g.,activin A, activin B, GDF1, GDF3, or Nodal); (b) decreases thephosphorylation of Smads (e.g., Smad2 and/or Smad3) in cells expressingActRIIA in the presence of an ActRIIA ligand (e.g., activin A); (c)decreases the phosphorylation of ALK4 and/or ALK7 in cells expressingActRIIA and ALK4 and/or ALK7 in the presence of an ActRIIA ligand; and(d) binds to ActRIIA with a K_(D) of ≤1 nM and ≥1 pM (e.g., asdetermined by BIACORE® analysis). In some aspects, the ActRIIA-bindingprotein has 2, 3, or 4 of the above characteristics. In some aspects,the ActRIIA-binding protein has at least 2 or at least 3 of the abovecharacteristics.

In some aspects, the ActRII-binding protein is an antibody thatspecifically binds ActRII. In some aspects, the anti-ActRII specificallybinds ActRIIB and/or ActRIIA. In some aspects, the anti-ActRII antibodyis a murine antibody, a humanized antibody, a chimeric antibody, amonoclonal antibody, a polyclonal antibody, a recombinant antibody, amultispecific antibody, or any combination thereof. In some aspects theanti-ActRII antibody is an Fv fragment, an Fab fragment, an F(ab′)2fragment, an Fab′ fragment, a dsFv fragment, an scFv fragment, or ansc(Fv)2 fragment.

In some aspects, the ActRII-binding protein specifically binds ActRII(e.g., ActRIIA and/or ActRIIB) and blocks an activity of anActRII-ligand (e.g., GDF8 (myostatin) and/or activin). In some aspectsthe ActRII-binding protein specifically binds ActRII (e.g., anddecreases the inhibition of muscle formation or the increase in fatformation associated with the activity of an ActRII ligand (e.g., GDF8(myostatin and/or activin). In some aspects the ActRII-binding proteinspecifically binds ActRII and treats or ameliorates one or moreconditions associated with a muscle disorder or a metabolic disorder. Insome aspects, the muscle disorder is muscle wasting due to disease ordisuse. In some aspects, the metabolic disorder is diabetes, obesity,hyperglycemia, or bone loss.

In particular aspects, the ActRIIB-binding protein (e.g., ananti-ActRIIB antibody or an anti-ActRIIB and ActRIIA antibody) inhibitsor decreases the binding of ActRIIB by GDF8 (myostatin) or GDF8-mediatedActRIIB Smad signaling. In another aspect, the ActRIIB-binding proteindecreases the inhibition of muscle formation or the increase in fatformation. In some aspects the ActRIIB-binding protein binds ActRIIB andinhibits or decreases one or more conditions associated with a muscledisorder or a metabolic disorder. In some aspects, the muscle disorderis muscle wasting due to disease or disuse. In some aspects, themetabolic disorder is diabetes, obesity, hyperglycemia, or bone loss.increases muscle mass or strength in a subject.

In certain aspects, the blocking of ActRII (e.g., ActRIIB and/orActRIIA) activity by an ActRII-binding protein (e.g., an anti-ActRIIBantibody and an anti-ActRIIA antibody) described herein, inhibits ordecreases one or more conditions associated with a muscle disorder, suchas muscle wasting. In further aspects the blocking of ActRII inhibits ordecreases one or more conditions associated with muscle wasting due todisease or disuse. In particular aspects, the ActRII-binding protein(e.g., an anti-ActRIIB antibody or an anti-ActRIIB and ActRIIA antibody)inhibits or decreases the binding to ActRIIB by GDF8. In another aspectthe ActRIIB-binding protein inhibits or decreases the inhibition ofmuscle differentiation by a Smad-dependent pathway.

In some aspects, the ActRII-binding protein specifically binds ActRIIBand blocks an ActRIIB ligand-mediated activity. Some ActRIIB ligandssuch as GDF-8 are known to be a negative regulator of skeletal muscletissue and myostatin signaling is known to lead to muscle mass. ActRIIBligand-mediated signalling can also modulate the production ofmuscle-specific enzymes (e.g., creatine kinase), stimulate myoblastproliferation, and modulate preadipocyte differentiation to adipocytes.Increased myostatin activity has been associated with muscle wastingdisorders, muscle loss due to inactivity, and metabolic disordersincluding diabetes, obesity, hyperglycemia, and bone loss. IncreasedActRIIB ligand-mediated activity has also been associated withage-related increases in fat to muscle ratios, and age-related muscularatrophy. In some aspects the ActRII-binding protein specifically bindsActRIIB and decreases the inhibition of muscle formation or the increasein fat formation associated with the activity of some ActRIIB ligands.In some aspects the ActRII-binding protein specifically binds ActRIIBand treats or ameliorates one or more conditions associated with amuscle disorder or a metabolic disorder. In some aspects, the muscledisorder is muscle wasting due to disease or disuse. In some aspects,the metabolic disorder is diabetes, obesity, hyperglycemia, or boneloss. ActRIIB ligand-mediated activity can be determined usingart-recognized methods, such as those described herein.

In certain aspects, the blocking of ActRII (e.g., ActRIIB and/orActRIIA) activity by an ActRII-binding protein (e.g., an anti-ActRIIBantibody and an anti-ActRIIA antibody) described herein, reduces one ormore conditions associated with fibrosis. In particular aspects, theActRIIB-binding protein inhibits or decreases ActRIIB-mediateddevelopment of fibrotic lesions, weight loss or other clinical symptoms,and/or altered expression of biological molecules (e.g., mRNA or proteinexpression) associated with the development of a fibrotic condition. Inparticular aspects, the ActRIIA-binding protein inhibits or decreasesActRIIA-mediated development of fibrotic lesions, weight loss or otherclinical symptoms, and/or altered expression of biological molecules(e.g., mRNA or protein expression) associated with the development of afibrotic condition.

As noted above, an anti-ActRII antibody (e.g., a full-lengthActRIIB-antibody and an ActRII-binding antibody fragment, and a variantand derivative thereof) containing a VH and/or VL amino acid sequencethat binds ActRII can have at least 85%, 90%, 95%, 96%, 97%, 98% or 99%sequence identity to a sequence set forth herein. In some aspects, theVH and/or VL amino acid sequence(s) that binds ActRII comprise 8, 7, 6,5, 4, 3, 2, 1 amino acid additions, substitutions (e.g., conservativesubstitutions) or deletions relative to a sequence set forth herein. Inadditional aspects, the VH and/or VL amino acid sequence that bindsActRII comprise 1, 2, 3, 4, 5 or more amino acid additions,substitutions (e.g., conservative substitutions) or deletions relativeto a sequence set forth herein. An anti-ActRII antibody containing VHand VL regions having a certain percent similarity to a VH region or VLregion, or having one or more substitutions, deletions and/or insertions(e.g., conservative substitutions) can be obtained by mutagenesis (e.g.,site-directed or PCR-mediated mutagenesis) of nucleic acid moleculesencoding VH and/or VL regions described herein, followed by testing ofthe encoded altered antibody for binding to ActRII and optionallytesting for retained function using the functional assays describedherein or an assay known in the art that can routinely be modified totest the retained function.

The affinity or avidity of an ActRII-binding protein such as, ananti-ActRIIB antibody (e.g., a full-length ActRIIB-antibody and anActRII-binding antibody fragment, and a variant and derivative thereof),for hActRIIB, murActRIIB, can be determined experimentally using anysuitable method known in the art, e.g., flow cytometry, enzyme-linkedimmunosorbent assay (ELISA), or radioimmunoassay (RIA), or kinetics(e.g., BIACORE® or KINEXA® analysis). Direct binding assays andcompetitive binding assay formats can be readily employed. (See, forexample, Berzofsky et al., “Antibody-Antigen Interactions,” InFundamental Immunology, Paul, W. E., Ed., Raven Press: New York, N.Y.(1984); Kuby, Immunology, W. H. Freeman and Company: New York, N.Y.(1992); and methods described herein.) The measured affinity of aparticular antibody-antigen interaction can vary if measured underdifferent conditions (e.g., salt concentration, pH, temperature). Thus,measurements of affinity and other ActRII-binding parameters (e.g.,K_(D) or Kd, K_(on), K_(off)) are made with standardized solutions ofActRII-binding proteins and ActRII and the measurements are performedusing standardized conditions and methods, as described herein orotherwise known in the art.

The disclosure further provides an ActRII-binding protein such as, ananti-ActRIIB antibody and/or an Anti-ActRIIA antibody as describedherein, where the ActRII-binding protein is conjugated to a heterologousagent. In certain aspects the heterologous agent is an antimicrobialagent, a therapeutic agent, a prodrug, a peptide, a protein, an enzyme,a lipid, a biological response modifier, a pharmaceutical agent, alymphokine, a heterologous antibody or antibody fragment, a detectablelabel, or a polyethylene glycol (PEG). Heteroconjugate ActRII-bindingproteins are discussed in more detail elsewhere herein.

In certain aspects, the ActRII-binding protein is not an anti-ActRIIantibody. A variety of methods for identifying and producingnon-antibody polypeptides that bind with high affinity to a proteintarget are known in the art. See, e.g., Skerra, Curr. Opin. Biotech.18:295-304 (2007); Hosse et al., Protein Science 15:14-27 (2006); Gillet al., Curr. Opin. Biotechnol. 17:653-658 (2006); Nygren, FEBS J.275:2668-2676 (2008); and Skerra, FEBS J. 275:2677-2683 (2008), each ofwhich is incorporated by reference herein in its entirety. In someaspects, phage display technology can been used to identify/produce anActRII-binding protein. In some aspects, the ActRII-binding proteincomprises a protein scaffold based on a type selected from the groupconsisting of VASP polypeptides, avian pancreatic polypeptide (aPP),tetranectin (based on CTLD3), affilin (based onγB-crystallin/ubiquitin), a knottin, an SH3 domain, a PDZ domain,tendamistat, transferrin, an ankyrin consensus repeat domain (e.g.,DARPins), a lipocalin protein fold (e.g., anticalins and Duocalins), aProtein Epitope Mimetic (PEM), a maxybody/avimer, a domain antibody afibronectin domain (e.g., 10 Fn3, see, e.g., U.S. Appl. Publ. Nos.2003/0170753 and 20090155275, each of which is herein incorporated byreference in its entirety), a domain of protein A (e.g., Affibodies),and thioredoxin.

In some aspects the disclosure provides an ActRIIA-binding protein(e.g., an anti-ActRIIA antibody such as, a full-length anti-ActRIIAantibody and an ActRIIA-binding antibody fragment) that competes forbinding ActRIIA with an anti-ActRIIA antibody provided herein. In someaspects the disclosure provides an ActRIIA-binding protein that binds tothe same epitope of ActRIIA as an ActRIIA-binding protein providedherein.

In some aspects the disclosure provides an ActRIIB-binding protein(e.g., an anti-ActRIIB antibody such as, a full-length anti-ActRIIBantibody and an ActRIIB-binding antibody fragment) that competes forbinding ActRIIB with an anti-ActRIIB antibody provided herein. In someaspects the disclosure provides an ActRIIB-binding protein that binds tothe same epitope of ActRIIB as an ActRIIB-binding protein providedherein. The ability of a test ActRII-binding protein to inhibit thebinding of, for example, a reference binding protein such as an antibodycomprising a VH sequence of SEQ ID NO:40 and a VL sequence of SEQ IDNO:9, or a VH sequence of SEQ ID NO:119 and a VL sequence of SEQ IDNO:91, to ActRIIB demonstrates that the test ActRII-binding protein cancompete with the reference antibody for binding to ActRIIB. Such anActRIIB-binding protein can, according to non-limiting theory, bind tothe same or a related (e.g., a structurally similar or spatiallyproximal) epitope on ActRIIB as the ActRIIB-reference antibody withwhich it competes. In one aspect, the ActRIIB-binding protein binds tothe same epitope on ActRIIB as an antibody comprising a VH sequence ofSEQ ID NO:40 and a VL sequence of SEQ ID NO:9.

ActRII receptors such as, ActRIIB and ActRIIA, are known tophosphorylate ActRI coreceptors (e.g., Alk4 and Alk7) and to signalthrough the phosphorylation of Smads (e.g., Smad2 and/or Smad3). In someaspects, an ActRII-binding protein (e.g., an anti-ActRIIB antibody andan anti-ActRIIA antibody) can decrease ActRII-mediated phosphorylationof its cognate ActRI receptor. In some aspects, an ActRIIB-bindingprotein (e.g., an anti-ActRIIB antibody) can decrease ActRIIB-mediatedphosphorylation of ALK4 and/or ALK7. In some aspects, an ActRIIA-bindingprotein (e.g., an anti-ActRIIA antibody) can decrease ActRIIA-mediatedphosphorylation of ALK4 and/or ALK7. In some aspects, an ActRII-bindingprotein can inhibit ActRII-mediated Smads (e.g., Smad2 and/or Smad3)phosphorylation in ActRII2-expressing cells. In some aspects, anActRIIB-binding protein (e.g., an anti-ActRIIB antibody) can decreaseActRIIB-mediated Smads (e.g., Smad2 and/or Smad3) phosphorylation incell expressing ActRIIB. In some aspects, an ActRIIA-binding protein(e.g., an anti-ActRIIA antibody) can decrease ActRIIA-mediated Smads(e.g., Smad2 and/or Smad3) phosphorylation in cell expressing ActRIIA.In some aspects the ActRII receptor expressing cells are human.

In some aspects, an ActRII-binding protein has at least onecharacteristic selected from: (a) competing with activin A for bindingto ActRIIA and/or ActRIIB; (b) decreasing the phosphorylation of Smads(e.g., Smad2 and/or Smad3) in cells expressing ActRIIA and/or ActRIIB inthe presence of an ActRIIA and/or ActRIIB ligand (e.g., activin A); (c)decreasing the phosphorylation of ALK4 and/or ALK7 in cells expressingActRIIA and/or ActRIIB and ALK4 and/or ALK7 in the presence of anActRIIB and/or ActRIIA ligand; and (d) binding to ActRIIA and/or ActRIIBwith a K_(D) of ≤1 nM and ≥1 pM as determined by BIACORE® or by KINEXA®.

In some aspects, an ActRII-binding protein (e.g., an anti-ActRIIantibody) suppresses ActRII-mediated phosphorylation of an ActRIreceptor (e.g., ALK4 and/or ALK7), or the phosphorylation of Smads(e.g., Smad2 and/or Smad3) in cells expressing ActRII as measured usinga cell-based assay. In some aspects, an ActRII-binding proteinsuppresses ActRII-mediated phosphorylation with an IC₅₀ lower than 500pM, lower than 350 pM, lower than 250 pM, lower than 150 pM, lower than100 pM, lower than 75 pM, lower than 60 pM, lower than 50 pM, lower than40 pM, lower than 30 pM, lower than 20 pM, lower than 15 pM, lower than10 pM, or lower than 5 pM, as measured using a cell-based assay.

Preparation of ActRII-Binding Proteins

In some aspects, the ActRII-binding protein binds the extracellulardomain of ActRII (e.g., ActRIIB and ActRIIA). In further aspects, theActRII-binding protein is an anti-ActRIIA antibody and/or ananti-ActRIIB antibody such as, a full-length anti-ActRIIA antibody and afull-length anti-ActRIIB antibody and an ActRII-binding antibodyfragment, and variants, and derivatives thereof.

ActRII-binding proteins can be readily prepared using known techniques.Monoclonal anti-ActRII (e.g., ActRIIB and ActRIIA) antibodies can beprepared using techniques known in the art, including hybridoma methods,such as those described by Kohler and Milstein, Nature 256:495-497(1975). Using the hybridoma method, a mouse, hamster, or otherappropriate host animal, is immunized as described above to elicit theproduction by lymphocytes of antibodies that will specifically bind toan immunizing antigen. Lymphocytes can also be immunized in vitro.Following immunization, the lymphocytes are isolated and fused with asuitable myeloma cell line to form hybridoma cells that can then beselected away from unfused lymphocytes and myeloma cells. Hybridomasthat produce monoclonal antibodies directed specifically against ActRIIsuch as hActRIIB and hActRIIA, as determined by immunoprecipitation,immunoblotting, or by an in vitro binding assay (e.g., radioimmunoassay(RIA); enzyme-linked immunosorbent assay (ELISA)) can then be propagatedeither in in vitro culture using standard methods (see, e.g., Goding,Monoclonal Antibodies: Principles and Practice, Academic Press, 1986) orin vivo as ascites tumors in an animal. The monoclonal antibodies canthen be purified from the culture medium or ascites fluid as describedfor polyclonal antibodies above.

The provided monoclonal antibodies can also be made using recombinantDNA methods as described in U.S. Pat. No. 4,816,567, wherein thepolynucleotides encoding a monoclonal antibody are isolated from matureB-cells or a hybridoma cell, such as by RT-PCR using oligonucleotideprimers that specifically amplify the genes encoding the heavy and lightchains of the antibody, and their sequence is determined using knownprocedures. The isolated polynucleotides encoding the heavy and lightchains are then cloned into suitable expression vectors, which whentransfected into host cells such as E. coli cells, simian COS cells,Chinese hamster ovary (CHO) cells, Per.C6 cells, or myeloma cells (e.g.,NS0 cells) that do not otherwise produce immunoglobulin protein,monoclonal antibodies are generated by the host cells. Recombinantanti-ActRII monoclonal antibodies can also readily be isolated fromphage display libraries expressing CDRs of the desired species usingknown techniques (see, e.g., McCafferty et al., Nature 348:552-554(1990); Clackson et al., Nature 352:624-628 (1991); and Marks et al., J.Mol. Biol. 222:581-597 (1991)).

The anti-ActRII antibodies can optionally be humanized, resurfaced, andengineered to display high affinity for the ActRII antigen (e.g.,ActRIIB and ActRIIA) and other favorable biological properties. Forexample, a humanized (or human) anti-ActRII antibody, can readily bedesigned and prepared using commonly available three-dimensionalimmunoglobulin modeling and known procedures for selecting framework(FW) residues, consensus sequences, and germline sequences to provide adesired antibody characteristic, such as increased affinity for ActRII.

Affinity maturation strategies and chain shuffling strategies are knownin the art and can be employed to generate high affinity anti-ActRII(e.g., anti-ActRIIA and/or anti-ActRIIB) antibodies as well asderivatives and variants of the ActRII-binding proteins disclosedherein. See, e.g., Marks et al., Bio/Technology 10:779-783 (1992), whichis herein incorporated by reference in its entirety. An additionalstrategy for generating high affinity anti-ActRII (e.g., anti-ActRIIAand/or anti-ActRIIB) antibodies as well as derivatives and variants ofthe ActRII-binding proteins disclosed herein is to generate novel VH orVL regions carrying CDR-derived sequences of the disclosure using randommutagenesis of one or more selected VH and/or VL genes to generatemutations within the entire variable domain. Such a technique that useserror-prone PCR is described by Gram et al. (PNAS USA 89:3576-3580(1992)). In some embodiments, one or two amino acid substitutions aremade within a set of VH CDRs and/or VL CDRs. A further strategy useddirect mutagenesis to CDR regions of VH or VL genes encoding anti-ActRIIantibodies disclosed herein. Examples of such techniques are disclosedby Barbas et al. (PNAS USA 91:3809-3813 (1994)) and Schier et al. (J.Mol. Biol. 263:551-567 (1996)).

Humanization, resurfacing or engineering of anti-ActRII antibodies ofthe disclosure can be performed using any known method including, butnot limited to, those described in Jones et al., Nature 321:522 (1986);Riechmann et al., Nature 332:323 (1988); Verhoeyen et al., Science239:1534 (1988)), Sims et al., J. Immunol. 151: 2296 (1993); Chothia etal., J. Mol. Biol. 196:901 (1987), Carter et al., PNAS USA 89:4285(1992); Presta et al., J. Immunol. 151:2623 (1993), U.S. Pat. Nos.5,639,641, 5,723,323; 5,976,862; 5,824,514; 5,817,483; 5,814,476;5,763,192; 5,723,323; 5,766,886; 5,714,352; 6,204,023; 6,180,370;5,693,762; 5,530,101; 5,585,089; 5,225,539; 4,816,567, 7,557,189;7,538,195; and 7,342,110; Intl. Appl. Nos. PCT/US98/16280;PCT/US96/18978; PCT/US91/09630; PCT/US91/05939; PCT/US94/01234;PCT/GB89/01334; PCT/GB91/01134; PCT/GB92/01755; Intl. Appl. Publ. Nos.WO90/14443; WO90/14424; WO90/14430; and EP Pat. Publ. No. EP 229246;each of which is herein incorporated by reference in is entirely.Likewise, known assays are available for readily selectingActRII-antibodies displaying desirable features (e.g., assays fordetermining binding affinity to ActRII; cross-blocking assays such asthe BIACORE®-based human ActRII-binding protein competition bindingassays described herein).

Methods for engineering, humanizing or resurfacing non-human or humanantibodies can also be used and are known in the art. A humanized,resurfaced or similarly engineered antibody can have one or more aminoacid residues from a source that is non-human, e.g., but not limited to,mouse, rat, rabbit, non-human primate or other mammal. These non-humanamino acid residues are replaced by residues that are often referred toas “import” residues, which are typically taken from an “import”variable, constant or other domain of a known human sequence. Suchimported sequences can be used to reduce immunogenicity or reduce,enhance or modify binding, affinity, on-rate, off-rate, avidity,specificity, half-life, or any other suitable characteristic, as knownin the art. Preferably, part or all of the non-human or human CDRsequences are maintained while the non-human sequences of the variableand constant regions can be replaced with human or other amino acids.

The nucleic acid(s) encoding an ActRII-binding protein, such as afull-length anti-ActRIIA or anti-ActRIIB antibody can further bemodified in a number of different manners using recombinant DNAtechnology to generate alternative antibodies. In some aspects, nucleicacid(s) encoding the constant domains of the light and heavy chains of,for example, a mouse monoclonal antibody can be substituted (a) forthose coding regions of, for example, a human antibody to generate achimeric antibody or (b) for non-immunoglobulin encoding nucleic acid(s)to generate a fusion antibody. In some aspects, the constant regions aretruncated or removed to generate the desired antibody fragment of amonoclonal antibody. Site-directed or high-density mutagenesis of thevariable region coding sequence can be used to optimize specificity,affinity, etc. of a monoclonal antibody.

Anti-ActRII human antibodies can be directly prepared using any of thenumerous techniques known in the art. (See, e.g., Cole et al.,Monoclonal Antibodies and Cancer Therapy, Alan R. Liss, p. 77 (1985);Boemer et al., J. Immunol. 147(1):86-95 (1991); and U.S. Pat. No.5,750,373). Similarly, human anti-ActRII antibodies can readily beobtained from immortalized human B lymphocyte immunized in vitro orisolated from an immunized individual that produces an antibody directedagainst ActRII (e.g., ActRIIB and ActRIIA).

Human anti-ActRII antibodies can also be selected from a phage librarythat expresses human antibodies, as described, for example, in Vaughanet al., Nat. Biotech. 14:309-314 (1996), Sheets et al., PNAS95:6157-6162 (1998), Hoogenboom and Winter, J. Mol. Biol. 227:381(1991), and Marks et al., J. Mol. Biol. 222:581 (1991). Techniques forthe generating and screening antibody phage libraries are also describedin U.S. Pat. Nos. 5,969,108; 6,172,197; 5,885,793; 6,521,404; 6,544,731;6,555,313; 6,582,915; 6,593,081; 6,300,064; 6,653,068; 6,706,484; and7,264,963; and Rothe et al., J. Mol. Biol. 376(4):1182-1200 (2008)(eachof which is herein incorporated by reference in its entirety).

Human anti-ActRII antibodies can also be made in transgenic micecontaining human immunoglobulin loci that are capable upon immunizationof producing human antibodies in the absence of endogenousimmunoglobulin production. This approach is described for example, inU.S. Pat. Nos. 5,545,807; 5,545,806; 5,569,825; 5,625,126; 5,633,425;and 5,661,016.

Human anti-ActRII antibodies can also be selected and/or isolated fromyeast-based antibody presentation libraries, as disclosed in, forexample, WO012/009568; WO09/036379; WO10/105256; WO03/074679 and U.S.Appl. Publ. No. US2002/0177170, the contents of each of which is hereinincorporated by reference in its entirety. Such libraries are designedin silico to be reflective of the diversity afforded by the humanpreimmune repertoire.

Alternatively, anti-ActRII antibodies may be selected from ayeast-displayed antibody library see, for example: Blaise et al., Gene342(2):211-218 (2004); Boder et al., Nat Biotechnol. 15(6):553-557(1997); Kuroda et al., Biotechnol. Lett. 33(1):1-9 (2011). Review; Laueret al., J. Pharm. Sci. 101(1):102-15 (2012); Orcutt K. D. and Wittrup K.D. Antibody Engineering, yeast display and selections (2010), 207-233;Rakestraw et al., Protein Eng. Des. Sel. 24(6):525-30 (2011); and U.S.Pat. Nos. 6,423,538; 6,696,251; and 6,699,658.

Various techniques are known for the production of antigen-bindingantibody fragments. Traditionally, these fragments are derived viaproteolytic digestion of intact antibodies (see, e.g., Morimoto et al.,J. Biochem. Biophys. Meth. 24:107-117 (1993); and Brennan et al.,Science 229:81 (1985)). In certain aspects an ActRII-binding antibodyfragment is produced recombinantly. Fab, Fv, and scFv antibody fragmentscan all be expressed in and secreted from E. coli or other host cells,thus allowing the production of large amounts of these fragments. Suchan ActRII-binding antibody fragment can additionally be isolated fromthe antibody phage libraries discussed above. In some aspects, theActRII-binding antibody fragment is a linear antibody as described inU.S. Pat. No. 5,641,870. Other techniques for the production ofantigen-binding antibody fragments are known in the art.

Known techniques can be readily adapted for the production ofsingle-chain antibodies that bind ActRII (see, e.g., U.S. Pat. No.4,946,778). In addition, known methods can routinely be adapted for theconstruction of Fab expression libraries (see, e.g., Huse et al.,Science 246:1275-1281 (1989)) to allow rapid and effectiveidentification of monoclonal Fab fragments with the desired specificityfor ActRII. ActRII-binding antibody fragment can be produced bytechniques known in the art including, but not limited to: (a) a F(ab′)2fragment produced by pepsin digestion of an antibody; (b) a Fab fragmentgenerated by reducing the disulfide bridges of an F(ab′)2 fragment, (c)a Fab fragment generated by the treatment of the anti-ActRII antibodywith papain and a reducing agent, and (d) Fv fragments.

In certain aspects, an ActRII-binding protein (e.g., an anti-ActRIIAantibody and/or an anti-ActRIIB antibody) can be modified in order toincrease its serum half-life. This can be achieved, for example, byincorporation of a salvage receptor binding epitope into theActRII-binding protein by mutation of an appropriate region in theActRII-binding protein or by incorporating the salvage receptor epitopeinto a peptide tag that is then fused to the ActRIIB-binding protein ateither end or in the middle (e.g., by DNA or peptide synthesis). Othermethods to increase the serum half-life of an ActRII-binding protein,e.g., conjugation to a heterologous molecule such as PEG are known inthe art.

Heteroconjugate ActRII-binding proteins (e.g., anti-ActRIIB antibodies,such as a full-length anti-ActRIIB antibodies and ActRIIB-bindingantibody fragments, and variants and derivatives thereof) are alsowithin the scope of the disclosure. Heteroconjugate ActRII-bindingproteins are composed of two covalently joined proteins. It iscontemplated that the heteroconjugate ActRII-binding proteins can beprepared in vitro using known methods in synthetic protein chemistry,including those involving crosslinking agents. For example, immunotoxinscan be constructed using a disulfide exchange reaction or by forming athioether bond. Examples of suitable reagents for this purpose includeiminothiolate and methyl-4-mercaptobutyrimidate.

ActRII-binding proteins can comprise any type of variable region thatprovides for the association of the antibody with ActRII (e.g., ActRIIBand ActRIIA). Such variable region can comprise or be derived from anymammal that can be induced to mount a humoral response and generateimmunoglobulins against the ActRII antigen. The variable region of ananti-ActRII antibody can be, for example, of human, murine, non-humanprimate (e.g., cynomolgus monkeys, macaques, etc.) or lupine origin. Insome aspects both the variable and constant regions of the modifiedanti-ActRII antibodies are human. In other aspects the variable regionsof compatible antibodies (usually derived from a non-human source) canbe engineered or specifically tailored to improve the binding propertiesor reduce the immunogenicity of the molecule. In this respect, variableregions useful according to the disclosure can be humanized or otherwisealtered through the inclusion of imported amino acid sequences usingaffinity maturation, mutagenesis procedures, chain shuffling strategiesand/or other methods described herein or otherwise know in the art.

In certain aspects, the variable domains in both the heavy and lightchains of an anti-ActRII antibody are altered by at least partialreplacement of one or more CDRs and/or by partial framework regionreplacement and sequence changing. Although the CDRs can be derived froman antibody of the same class or even subclass as the antibody fromwhich the framework regions are derived, it is envisaged that the CDRswill be derived from an antibody of different class and in certainaspects from an antibody from a different species. It is not necessaryto replace all of the CDRs with the complete CDRs from the donorvariable region to transfer the antigen-binding capacity of one variabledomain to another. Rather, it is only necessary to transfer thoseresidues that are necessary to maintain the activity of theantigen-binding site. It is well within the competence of those ofordinary skill in the art, to routinely obtain a functional antibodywith reduced immunogenicity. See, e.g., U.S. Pat. Nos. 5,585,089,5,693,761 and 5,693,762.

Alterations to the variable region notwithstanding, those of ordinaryskill in the art will appreciate that the modified anti-ActRII of thedisclosure will comprise antibodies in which at least a fraction of oneor more of the constant region domains has been deleted or otherwisealtered so as to provide desired biochemical characteristics such asdecreased ADCC or increased serum half-life when compared with anantibody of approximately the same immunogenicity comprising a native orunaltered constant region. In some aspects, the constant region of themodified anti-ActRII antibodies comprise a human constant region.Modifications to the constant region can include additions, deletions orsubstitutions of one or more amino acids in one or more domains. Themodified anti-ActRII antibodies disclosed herein can comprisealterations or modifications to one or more of the three heavy chainconstant domains (CH1, CH2 or CH3) and/or to the light chain constantdomain (CL). In some aspects, the modified anti-ActRII antibodiescomprise constant regions wherein one or more domains are partially orentirely deleted are contemplated. In some aspects, the modifiedanti-ActRII antibodies comprise domain deleted constructs or variantswherein the entire CH2 domain has been removed (ΔCH2 constructs). Insome aspects, the omitted constant region domain can be replaced by ashort amino acid spacer (e.g., 10 residues) that provides some of themolecular flexibility typically imparted by the absent constant region.

It is generally understood that the constant region mediates severaleffector functions. For example, binding of the C1 component ofcomplement to antibodies activates the complement system. Activation ofcomplement is important in the opsonization and lysis of cell pathogens.The activation of complement also stimulates the inflammatory responseand can also be involved in autoimmune hypersensitivity. Further,antibodies bind to cells via the Fc region, with a Fc receptor site onthe antibody Fc region binding to a Fc receptor (FcR) on a cell. Thereare a number of Fc receptors that are specific for different classes ofantibody, including IgG (gamma receptors), IgE (eta receptors), IgA(alpha receptors) and IgM (mu receptors). Binding of antibody to Fcreceptors on cell surfaces triggers a number of important and diversebiological responses including engulfment and destruction ofantibody-coated particles, clearance of immune complexes, lysis ofantibody-coated target cells by killer cells (called antibody-dependentcell-mediated cytotoxicity, or ADCC), release of inflammatory mediators,placental transfer and control of immunoglobulin production.

In certain aspects, an anti-ActRII antibody has an altered effectorfunction that, in turn, affects the biological profile of theadministered anti-ActRII antibody. For example, the deletion orinactivation (through point mutations or other means) of a constantregion domain can reduce Fc receptor binding of the circulating modifiedantibody. In other cases the constant region modifications, can moderatecomplement binding and thus reduce the serum half-life and nonspecificassociation of a conjugated cytotoxin. Yet other modifications of theconstant region can be used to eliminate disulfide linkages oroligosaccharide moieties that allow for enhanced localization due toincreased antigen specificity or antibody flexibility. Similarly,modifications to the constant region in accordance with this disclosurecan easily be made using biochemical or molecular engineering techniquesknown to those of ordinary skill in the art.

In some aspects, an ActRIIB-binding protein provided herein is an ActRIIantibody that does not have one or more effector functions. Forinstance, in some aspects, the anti-ActRII antibody has noantibody-dependent cellular cytoxicity (ADCC) activity and/or nocomplement-dependent cytoxicity (CDC) activity. In certain aspects, theanti-ActRII antibody does not bind to an Fc receptor and/or complementfactors. In certain aspects, the anti-ActRII antibody has no effectorfunction. Examples of Fc sequence engineering modifications that reduceor eliminate ADCC and/or CDC activity and Fc receptor and/or complementfactor binding are described herein or otherwise know in the art, as areassays and procedures for testing the same.

In some aspects, an anti-ActRII antibody is engineered to fuse the CH3domain directly to the hinge region of the respective modified antibody.In other constructs a peptide spacer is inserted between the hingeregion and the modified CH2 and/or CH3 domains. For example, compatibleconstructs can be expressed in which the CH2 domain has been deleted andthe remaining CH3 domain (modified or unmodified) is joined to the hingeregion with a 5-20 amino acid spacer. Such a spacer can be added, forinstance, to ensure that the regulatory elements of the constant domainremain free and accessible or that the hinge region remains flexible.Amino acid spacers can, in some cases, prove to be immunogenic andelicit an unwanted immune response against the construct. Accordingly,in certain aspects, any spacer added to the construct can be relativelynon-immunogenic, or even omitted altogether, so as to maintain thedesired biochemical qualities of the modified anti-ActRII.

In additional aspects anti-ActRII antibodies are modified by the partialdeletion or substitution of a few or even a single amino acid in aconstant region. For example, the mutation of a single amino acid inselected areas of the CH2 domain can be enough to substantially reduceFc binding and thereby. Similarly one or more constant region domainsthat control the effector function (e.g., complement C1Q binding) can befully or partially deleted. Such partial deletions of the constantregions can improve selected characteristics of the anti-ActRII antibody(e.g., serum half-life) while leaving other desirable functionsassociated with the corresponding constant region domain intact. In someaspects the constant regions of the anti-ActRII antibodies are modifiedthrough the mutation or substitution of one or more amino acids thatenhances the profile of the resulting construct. In this respect it ispossible to disrupt the activity provided by a conserved binding site(e.g., Fc binding) while substantially maintaining the configuration andimmunogenic profile of the modified anti-ActRII antibody. The disclosurealso provides an anti-ActRII antibody that contains the addition of oneor more amino acids to the constant region to enhance desirablecharacteristics such, as decreasing or increasing effector function orproviding attachments sites for one or more cytotoxin, labeling orcarbohydrate moieties. In such aspects it can be desirable to insert orreplicate specific sequences derived from selected constant regiondomains.

The disclosure also provides an ActRII-binding protein that is a variantto the ActRIIB and ActRIIA-binding proteins provided herein (e.g.,murine, chimeric, humanized and human ActRII-binding proteins). Inparticular aspects, the variant ActRII-binding protein has at least onecharacteristic selected from the group consisting of: (a) competing withactivin A for binding to ActRIIB and/or ActRIIA; (b) decreasing thephosphorylation of Smads (e.g., Smad2 and/or Smad3) in cells expressingActRIIB and/or ActRIIA in the presence of an ActRIIB and/or ActRIIAligand (e.g., activin A); (c) decreasing the phosphorylation of ALK4and/or ALK7 in cells expressing ActRIIB and/or ActRIIA and ALK4 and/orALK7 in the presence of an ActRIIB and/or ActRIIA ligand; and (d)binding to ActRIIB or ActRIIA with a K_(D) of ≤1 nM and ≥1 pM (e.g., asdetermined by BIACORE® analysis). In some aspects, the ActRII-bindingprotein has 2, 3, or 4 of the above characteristics. In some aspects,the ActRII-binding protein has at least 2 or at least 3 of the abovecharacteristics. In further aspects, the variant contains conservativeamino acid residue substitution mutations compared to an ActRII-bindingprotein provided herein.

The provided ActRII-binding proteins, such as anti-ActRII antibodies,can be derivatized to contain additional chemical moieties known in theart for improving for example, the solubility, biological half-life,bioavailability, and to otherwise improve the stability, formulationand/or therapeutic properties of the ActRII-binding protein. Anon-exhaustive overview for such moieties can be found for example, inRemington's Pharmaceutical Sciences, 20th ed., Mack Publishing Co.,Easton, Pa. (2000).

Nucleic Acids Encoding ActRII-Binding Proteins and their Expression

Nucleic acid molecules and combinations of nucleic acid molecules thatencode an ActRII-binding protein are also provided. In some aspects, thenucleic acids molecules encode an anti-ActRII antibody, such as afull-length anti-ActRII antibody and an ActRII-binding antibodyfragment. In further aspects, the disclosure provides nucleic acidmolecules that encode a variant or derivative of a full-lengthanti-ActRII antibody or an ActRII-binding antibody fragment providedherein.

The nucleic acid molecules disclosed herein can be in the form of RNA orin the form of DNA. DNA includes cDNA, genomic DNA, and synthetic DNA;and can be double-stranded or single-stranded, and if single strandedcan be the coding strand/or non-coding (anti-sense) strand. In certainaspects, the nucleic acid molecule is isolated. In additional aspects, anucleic acid molecule is substantially pure. In some aspects the nucleicacid is cDNA or is derived from cDNA. In some aspects the nucleic acidis be recombinantly produced.

In some aspects, the nucleic acid molecule comprises an ActRII-bindingprotein coding sequence operably linked to a control sequence thatcontrols the expression of the coding sequence in a host cell or invitro. In particular aspects, the coding sequence is a cDNA. Thedisclosure also relates to vectors containing nucleic acid moleculescomprises an ActRII-binding protein coding sequence operably linked to acontrol sequence that controls the expression of the coding sequence ina host cell or in vitro.

In some aspects, the nucleic acid molecule comprises a coding sequencefor a mature ActRII-binding protein that is fused in the same readingframe to a heterologous polynucleotide sequence. In some aspects, theheterologous polynucleotide sequence encodes a leader peptide sequencethat facilitates the secretion of the expressed protein from the hostcell transformed with the ActRII-binding protein encoding nucleic acidmolecule(s). A protein containing a leader sequence is referred to as apreprotein and can have the leader sequence cleaved by the host cell toform the mature form of the ActRII-binding protein. Such leader peptidesequences and their use facilitating the secretion of recombinantproteins in host cells is generally known in the art. In additionalaspects, the heterologous polynucleotide sequence encodes additional 5′amino acid residues that can function for example, to facilitatepurification, add or improve protein stability and/or therapeutic ordiagnostic properties of the recombinantly expressed ActRII-bindingprotein.

In some aspects the disclosure provides isolated nucleic acids such asan ActRII-binding protein encoding cDNA fragments, sufficient for use asa hybridization probe, PCR primer or sequencing primer.

In some aspects, the nucleic acid molecules encode an ActRII-bindingprotein that has at least one characteristic selected from the groupconsisting of: (a) competes with an ActRII ligand for binding to theActRII; (b) decreases the phosphorylation of ALK4 and/or ALK7 in cellsexpressing an ActRII and a cognate ActRI in the presence of an ActRIIligand; (c) decreases the phosphorylation of one or more Smads in cellsexpressing ActRII in the presence of an ActRII ligand; and (d) binds toActRII with a K_(D) of ≤1 nM and ≥1 pM (e.g., as determined by BIACORE®analysis). In some aspects, the encoded ActRII-binding protein has 2, 3,or 4 of the above characteristics. In some aspects, the encodedActRII-binding protein has at least 2 or at least 3 of the abovecharacteristics. In some aspects, the encoded ActRII-binding proteincompetes for binding to ActRII with an antibody having an ActRII-bindingVH and VL pair disclosed herein. In additional aspects, the encodedActRII-binding protein binds to the same epitope of ActRII as anantibody disclosed herein.

In some aspects, the nucleic acid molecules encode an ActRII-bindingprotein that specifically binds ActRIIA and has at least onecharacteristic selected from the group consisting of: (a) competes withan ActRIIA ligand (e.g., activin A, activin B, GDF1, GDF3, or Nodal);(b) decreases the phosphorylation of ALK4 and/or ALK7 in cellsexpressing ActRIIA and ALK4 and/or ALK7 in the presence of an ActRIIAligand (e.g., activin A); (c) decreases the phosphorylation of one ormore Smads in cells expressing ActRIIA in the presence of an ActRIIAligand; and (d) binds to ActRIIA with a K_(D) of ≤1 nM and ≥1 pM (e.g.,as determined by BIACORE® analysis). In some aspects, the encodedActRIIA-binding protein has 2, 3, or 4 of the above characteristics. Insome aspects, the encoded ActRIIA-binding protein has at least 2 or atleast 3 of the above characteristics. In some aspects, the encodedActRIIA-binding protein competes for binding to ActRIIA with an antibodyhaving an ActRIIA-binding VH and VL pair disclosed herein. In additionalaspects, the encoded ActRIIA-binding protein binds to the same epitopeof ActRIIA as an antibody disclosed herein. In further aspects, thenucleic acid molecules encode an ActRIIA-binding protein thatspecifically binds ActRII and comprises a VH and a VL.

In some aspects, the nucleic acid molecules encode an ActRII-bindingprotein that specifically binds ActRIIB and has at least onecharacteristic selected from the group consisting of: (a) competes withactivin A and/or GDF8 for binding to ActRIIB; (b) decreases thephosphorylation of ALK4 and/or ALK7 in cells expressing ActRIIB and ALK4and/or ALK7 in the presence of an ActRIIB ligand (e.g., activin A and/orGDF8); (c) decreases the phosphorylation of one or more Smads in cellsexpressing ActRIIB in the presence of an ActRIIB ligand; and (d) bindsto ActRIIB with a K_(D) of ≤1 nM and ≥1 pM (e.g., as determined byBIACORE® analysis). In some aspects, the encoded ActRIIB-binding proteinhas 2, 3, or 4 of the above characteristics. In some aspects, theencoded ActRIIB-binding protein has at least 2 or at least 3 of theabove characteristics. In some aspects, the encoded ActRIIB-bindingprotein competes for binding to ActRIIB with an antibody having anActRIIB-binding VH and VL pair disclosed herein. In additional aspects,the encoded ActRIIB-binding protein binds to the same epitope of ActRIIBas an antibody disclosed herein. In further aspects, the nucleic acidmolecules encode an ActRIIB-binding protein that specifically bindsActRIIB and comprises a VH and a VL

In some aspects, the nucleic acid molecules encode an ActRII-bindingprotein that specifically binds ActRIIB and ActRIIA and has at least onecharacteristic selected from the group consisting of: (a) competes withactivin A and/or GDF8 for binding to ActRIIB and ActRIIA; (b) decreasesthe phosphorylation of ALK4 and/or ALK7 in cells expressing ActRIIAand/or ActRIIB and ALK4 and/or ALK7 in the presence of an ActRIIA and/orActRIIB ligand (e.g., activin A and/or GDF8); (c) decreases thephosphorylation of one or more Smads in cells expressing ActRIIA and/orActRIIB in the presence of an ActRIIA and/or ActRIIB ligand; and (d)binds to ActRIIA or ActRIIB with a K_(D) of ≤1 nM and ≥1 pM (e.g., asdetermined by BIACORE® analysis). In some aspects, the encoded ActRIIBand ActRIIA-binding protein has 2, 3, or 4 of the above characteristics.In some aspects, the encoded ActRIIB-binding protein has at least 2 orat least 3 of the above characteristics. In some aspects, the encodedActRIIB and ActRIIA-binding protein competes for binding to ActRIIB andActRIIA with an antibody having an ActRIIB and ActRIIA-binding VH and VLpair disclosed herein. In additional aspects, the encodedActRIIB-binding protein binds to the same epitope of ActRIIA or ActRIIBas an antibody disclosed herein. In further aspects, the nucleic acidmolecules encode an ActRIIB and ActRIIA-binding protein thatspecifically binds ActRIIB and ActRIIA and comprises a VH and a VL.

The disclosure also provides vectors and sets of vectors containingnucleic acids and sets of nucleic acids encoding the ActRIIB-bindingproteins provided herein. Host cells transformed with these nucleicacids, sets of nucleic acids, vectors, and sets of vectors are alsoprovided, as are methods of making an using the ActRII-binding proteins.

In some aspects, the disclosure provides a host cell comprising anucleic acid molecule or combination of nucleic acid molecules or avector as provided above, where the host cell can, in some instancesexpress an ActRII-binding protein (e.g., an anti-ActRII antibody suchas, a full-length ActRIIB-antibody and an ActRII-binding antibodyfragment), that specifically binds to ActRII. In further aspects, thedisclosure provides a host cell transformed with a nucleic acid moleculeor combination of nucleic acid molecules or a vector as provided above,where the host cell can, in some instances express an ActRII-bindingprotein that specifically binds to ActRII. Such host cells can beutilized in a method of making an ActRII-binding protein as providedherein, where the method includes (a) culturing the host cell and (b)isolating the ActRII-binding proteins expressed from the host cell.

The disclosure also provides a method for making an ActRII-bindingprotein comprising culturing a host cell (e.g., a hybridoma ortransformed mammalian host cell) capable of expressing theActRII-binding protein under suitable conditions and optionally providesa method for isolating the ActRII-binding protein secreted from the hostcell. And the disclosure additionally provides the ActRII-bindingprotein isolated using the disclosed methods.

In certain aspects the polynucleotides comprise the coding sequence(s)for the mature ActRII-binding protein(s) (e.g., an ActRII-antibody, suchas a full-length antibody and an ActRII-binding antibody fragment) fusedin the same reading frame to a marker sequence that allows, for example,for purification of the encoded polypeptide. For example, the markersequence can be a hexa-histidine tag (SEQ ID NO: 179) supplied by apQE-9 vector to provide for purification of the mature polypeptide fusedto the marker in the case of a bacterial host, or the marker sequencecan be a hemagglutinin (HA) tag derived from the influenza hemagglutininprotein when a mammalian host (e.g., COS-7 cells) is used.

Nucleic acid variants encoding an ActRII-binding protein such as, ananti-ActRII antibody and an ActRII-binding antibody fragment, are alsoprovided. Nucleic acid variants can contain alterations in the codingregions, non-coding regions, or both. In some aspects the nucleic acidvariants contain alterations that produce silent substitutions,additions, or deletions, but do not alter the properties or activitiesof the encoded polypeptide. In some aspects, the nucleic acid variantsare produced by silent substitutions due to the degeneracy of thegenetic code. Nucleic acid variants can be produced for a variety ofreasons, e.g., to optimize codon expression for a particular host(change codons in the human mRNA to those preferred by a bacterial hostsuch as E. coli). Vectors and cells comprising the nucleic acidsdescribed herein are also provided.

In some aspects a nucleic acid sequence encoding an ActRII-bindingprotein (e.g., an anti-ActRII antibody such as a full-length antibodyand an ActRII-binding antibody fragment) is constructed by chemicalsynthesis using an oligonucleotide synthesizer. Such oligonucleotidescan be designed based on the amino acid sequence of the desiredpolypeptide and codon optimization based on the host cell preferences.Standard methods can routinely be applied to synthesize an isolatepolynucleotide sequences encoding ActRII-binding proteins.

Once assembled (by synthesis, site-directed mutagenesis or anothermethod), the nucleic acid sequences encoding ActRII-binding proteins canroutinely be operably linked to a control sequence appropriate forexpression of the ActRII-binding proteins in a desired host. In someaspects, the nucleic acid sequences encoding ActRII-binding proteins isinserted into an expression vector and operably linked to a controlsequence appropriate for expression of the protein in a desired host. Inorder to obtain high expression levels of a transfected gene in a host,the gene can be operably linked to or associated with transcriptionaland translational expression control sequences that are functional inthe chosen expression host.

In certain aspects, recombinant expression vectors are used to amplifyand express DNA encoding an ActRII-binding protein, such as, ananti-ActRIIB antibody, an anti-ActRIIA antibody, an ActRIIB-bindingantibody fragment, or an ActRIIA-binding antibody fragment. Recombinantexpression vectors are replicable DNA constructs which have synthetic orcDNA-derived DNA fragments encoding a polypeptide chain of anActRII-binding protein operably linked to suitable transcriptional ortranslational regulatory elements derived from mammalian, microbial,viral or insect genes. A transcriptional unit generally comprises anassembly of (1) a genetic element or elements having a regulatory rolein gene expression, for example, transcriptional promoters or enhancers,(2) a structural or coding sequence which is transcribed into mRNA andtranslated into protein, and (3) appropriate transcription andtranslation initiation and termination sequences, as described in detailbelow. Such regulatory elements can include an operator sequence tocontrol transcription. The ability to replicate in a host, usuallyconferred by an origin of replication, and a selection gene tofacilitate recognition of transformants can additionally beincorporated. DNA regions are operably linked when they are functionallyrelated to each other. For example, DNA for a signal peptide (secretoryleader) is operably linked to DNA for a polypeptide if it is expressedas a precursor which participates in the secretion of the polypeptide; apromoter is operably linked to a coding sequence if it controls thetranscription of the sequence; or a ribosome binding site is operablylinked to a coding sequence if it is positioned so as to permittranslation. Structural elements intended for use in yeast expressionsystems include a leader sequence enabling extracellular secretion oftranslated protein by a host cell. Alternatively, where a recombinantprotein is expressed without a leader or transport sequence, the proteincan include an N-terminal methionine residue. This residue canoptionally be subsequently cleaved from the expressed recombinantprotein to provide a final protein. In certain aspects, the disclosureprovides a composition, e.g., a pharmaceutical composition, comprising anucleic acid or vector of as described above or elsewhere herein,optionally further comprising one or more carriers, diluents,excipients, or other additives.

Also provided is a host cell transformed with the nucleic acid moleculeor cDNA molecules and/or the vectors disclosed herein. The disclosurealso provides host cells transformed with the disclosed nucleic acidmolecule or molecules operably linked to a control sequence andoptionally inserted into a vector. In some aspects, the host cell is amammalian host cell. In further aspects, the mammalian host cell is aNS0 murine myeloma cell, a PER.C6® human cell, or a Chinese hamsterovary (CHO) cell. In other aspects, the host cell is a hybridoma.

In additional aspects, the disclosure provides a method of making anActRII-binding protein (e.g., an anti-ActRII antibody such as, afull-length ActRII-antibody and an ActRII-binding antibody fragment, andvariants and derivatives thereof) provided herein comprising culturing atransformed host cell or a hybridoma disclosed herein under suitableconditions for producing the ActRII-binding protein. The disclosureoptionally provides isolating the ActRII-binding protein secreted fromthe host cell. The disclosure also optionally provides theActRII-binding protein produced using this method and pharmaceuticalcompositions comprising the ActRII-binding protein and apharmaceutically acceptable carrier.

The choice of expression control sequence and expression vector willdepend upon the choice of host. A wide variety of expression host/vectorcombinations can be employed. Useful expression vectors for eukaryotichosts, include, for example, vectors comprising expression controlsequences from SV40, bovine papilloma virus, adenovirus andcytomegalovirus. Useful expression vectors for bacterial hosts includeknown bacterial plasmids, such as plasmids from E. coli, including pCR1,pBR322, pMB9 and their derivatives, and also wider host range plasmids,such as M13 and filamentous single-stranded DNA phages.

Suitable host cells for expression of an ActRII-binding protein, includeprokaryotes, yeast, insect or higher eukaryotic cells under the controlof appropriate promoters. Prokaryotes include gram negative or grampositive organisms, for example E. coli or bacilli. Higher eukaryoticcells include established cell lines of mammalian origin as describedbelow. Cell-free translation systems could also be employed. Additionalinformation regarding methods of protein production, including antibodyproduction, can be found, e.g., in U.S. Appl. Publ. No. 2008/0187954,U.S. Pat. Nos. 6,413,746 and 6,660,501, and Intl. Appl. Publ. No.WO04/009823, each of which is herein incorporated by reference in itsentirety.

Various mammalian or insect cell culture systems can also beadvantageously employed to express recombinant ActRII-binding proteins(e.g., an anti-ActRII antibody such as, a full-length ActRII-antibodyand an ActRII-binding antibody fragment, and variants and derivativesthereof). Expression of recombinant ActRII-binding proteins in mammaliancells can be performed because such proteins are generally correctlyfolded, appropriately modified and completely functional. Examples ofsuitable mammalian host cell lines include HEK-293 and HEK-293T, theCOS-7 lines of monkey kidney cells, described by Gluzman (Cell 23:175(1981)), and other cell lines including, for example, L cells, C127,3T3, Chinese hamster ovary (CHO), HeLa and BHK cell lines. Mammalianexpression vectors can comprise nontranscribed elements such as anorigin of replication, a suitable promoter and enhancer linked to thegene to be expressed, and other 5′ or 3′ flanking nontranscribedsequences, and 5′ or 3′ nontranslated sequences, such as necessaryribosome binding sites, a polyadenylation site, splice donor andacceptor sites, and transcriptional termination sequences. Baculovirussystems for production of heterologous proteins in insect cells arereviewed by Luckow and Summers, BioTechnology 6:47 (1988).

ActRII-binding proteins produced by a transformed host cell or hybridomacan be purified according to any suitable method. Such standard methodsinclude chromatography (e.g., ion exchange, affinity and sizing columnchromatography), centrifugation, differential solubility, or by anyother standard technique for protein purification. Affinity tags such ashexahistidine (SEQ ID NO: 179), maltose binding domain, influenza coatsequence and glutathione-S-transferase can be attached to the protein toallow easy purification by passage over an appropriate affinity column.ActRII-binding proteins can also be physically characterized using suchtechniques as proteolysis, nuclear magnetic resonance and x-raycrystallography.

For example, supernatants from systems that secrete recombinantActRII-binding proteins into culture media can be first concentratedusing a commercially available protein concentration filter, forexample, an Amicon or Millipore Pellicon ultrafiltration unit. Followingthe concentration step, the concentrate can be applied to a suitablepurification matrix. Alternatively, an anion exchange resin can beemployed, for example, a matrix or substrate having pendantdiethylaminoethyl (DEAE) groups. The matrices can be acrylamide,agarose, dextran, cellulose or other types commonly employed in proteinpurification. Alternatively, a cation exchange step can be employed.Suitable cation exchangers include various insoluble matrices comprisingsulfopropyl or carboxymethyl groups. Finally, one or more reversed-phasehigh performance liquid chromatography (RP-HPLC) steps employinghydrophobic RP-HPLC media, e.g., silica gel having pendant methyl orother aliphatic groups, can be employed to further purify anActRII-binding protein. Some or all of the foregoing purification steps,in various combinations, can also routinely be employed to provide ahomogeneous recombinant ActRII-binding proteins.

A recombinant ActRII-binding protein (e.g., an anti-ActRII antibody suchas, a full-length ActRII-antibody and an ActRII-binding antibodyfragment and variants and derivatives thereof) produced in bacterialculture can be isolated, for example, by initial extraction from cellpellets, followed by one or more concentration, salting-out, aqueous ionexchange or size exclusion chromatography steps. High performance liquidchromatography (HPLC) can be employed for final purification steps.Microbial cells employed in expression of a recombinant protein can bedisrupted by any convenient method, including freeze-thaw cycling,sonication, mechanical disruption, or use of cell lysing agents.

Methods known in the art for purifying target binding proteins such asfull-length antibodies and antigen-binding antibody fragments alsoinclude, for example, those described in U.S. Appl. Publ. Nos.2008/0312425, 2008/0177048, and 2009/0187005, each of which isincorporated herein by reference herein in its entirety.

In certain aspects, the ActRII-binding protein is not an antibody. Avariety of methods are known for identifying and producing non-antibodypolypeptides that bind with high affinity to a protein target. See,e.g., Skerra, Curr. Opin. Biotechnol. 18:295-304 (2007), Hosse et al.,Protein Science 15:14-27 (2006), Gill et al., Curr. Opin. Biotechnol.17:653-658 (2006), Nygren, FEBS J. 275:2668-2676 (2008), and Skerra,FEBS J. 275:2677-2683 (2008), each of which is herein incorporated byreference in its entirety. In certain embodiments, phage displaytechnology is used to identify/produce the ActRII-binding protein. Incertain embodiments, the polypeptide comprises a protein scaffold of atype selected from the group consisting of protein A, a lipocalin, afibronectin domain (e.g., Fibronectin type III (Fn3)), an ankyrinconsensus repeat domain, and thioredoxin.

Methods of Use and Pharmaceutical Compositions

The provided ActRII-binding proteins (including antibodies,immunoconjugates, and polypeptides) are useful in a variety ofapplications including, but not limited to, diagnostic methods andmethods of treating and/or ameliorating various diseases and conditionswith an ActRII-binding protein (e.g., an anti-ActRIIB and an ActRIIAantibody). Methods are provided for the use of an ActRII-binding protein(e.g., an anti-ActRII antibody such as, a full-length antibody thatspecifically binds ActRII and an ActRII-binding antibody fragment, andvariants and derivatives thereof) to treat subjects having a disease orcondition associated with ActRII (e.g., ActRIIB and/or ActRIIA)signaling and/or increased ActRII expression. In additional aspects, thedisclosure provides a pharmaceutical composition containing anActRII-binding protein provided herein and a pharmaceutically acceptablecarrier. In some aspects, the disclosure provides a pharmaceuticalcomposition containing an ActRII-binding protein provided herein and apharmaceutically acceptable carrier, for use as a medicament. Thedisclosure also provides the use of the pharmaceutical compositionsdisclosed herein for treating and/or ameliorating a disease or conditionassociated with ActRII, increased ActRII expression and/or increasedActRII signaling. In some aspects, the disease or condition treatedusing the pharmaceutical composition provided herein is a muscledisorder, such as muscle wasting due to disease or disuse. In additionalaspects the disease or condition treated using the pharmaceuticalcompositions provided herein is a fibrotic condition (e.g., a hepatic,pulmonary, vascular and/or ocular fibrotic condition); an inflammatory,cardiovascular, pulmonary, musculoskeletal, neurologic, or metabolicdisease or condition; wound healing; or cancer.

In some aspects, a pharmaceutical composition contains an ActRII-bindingprotein (e.g., a full-length antibody that specifically binds ActRIIBand a full-length antibody that specifically binds ActRIIA) and apharmaceutically acceptable carrier, and further comprises a labelinggroup or an effector group. A “label” refers to one or more elements,isotopes, or chemical compounds attached to enable the detection in ascreen. Labels generally fall into three classes: (a) isotopic labels,which may be radioactive or heavy isotopes, (b) small molecule labels,which may include fluorescent and colorimetric dyes, or molecules suchas biotin that enable other labeling methods, and (c) immune labels,which may be an epitope incorporated as a fusion partner that isrecognized by an antibody, “Labeling group” refers to any detectablelabel. In some aspects, the labeling group is coupled to theActRII-binding protein via a spacer (e.g., a peptide spacer) to reducepotential steric hindrance. Labels may be incorporated into the compoundat any position and may be incorporated in vitro or in vivo duringprotein expression. Various methods for labeling proteins are known inthe art and may be used in performing the provided methods. Inadditional aspects, the labeling group is selected from the groupconsisting of: isotopic labels, magnetic labels, redox active moieties,optical dyes, biotinylated groups and polypeptide epitopes recognized bya secondary reporter. In some aspects, the labeling group is afluorescent protein such as a Green Fluorescent Protein or derivativethereof (e.g., enhanced GFP, blue fluorescent protein or derivativethereof (e.g., EBFP (Enhanced Blue Fluorescent Protein), EBFP2, Azurite,mKalama1, cyan fluorescent protein or derivative thereof (e.g., ECFP(Enhanced Cyan Fluorescent Protein), Cerulean, CyPet), yellowfluorescent protein or derivative thereof (e.g., YFP, Citrine, Venus,YPet). In some aspects, the polypeptide epitope is a member selectedfrom a biotin signaling peptide, histidine peptide (his), hemagglutinin(HA), Flag, gold binding peptide. In additional aspects the effectorgroup is selected from the group consisting of a radioisotope,radionucleotide, a toxin, a therapeutic and a chemotherapeutic agent.

The ActRII-binding proteins of the present disclosure have applicationsin in vitro and in vivo diagnostic and therapeutic utilities. Forexample, the ActRII-binding proteins can be administered to cells inculture, e.g., in vitro or in vivo, or in a subject, to treat, preventor diagnose a variety of diseases or conditions. In some aspects, theActRII-binding proteins are human antibodies, murine antibodies, orhumanized antibodies.

Also provided are methods of blocking ActRII activity. In some aspects,the method comprises contacting ActRII with an ActRII-binding protein.In some instances the method is performed in vivo. In other instances,the method is performed in vitro. In some aspects the blocked ActRIIactivity is selected from (a) binding by an ActRII ligand (e.g., activinA, activin B, GDF8 (myostatin), GDF11, BMP6, GDF3, BMP9, or BMP10); (b)phosphorylation of one or more Smads in cells expressing ActRII in thepresence of activin A; (c) phosphorylation of ALK4 and/or ALK7 in cellsexpressing ActRII, and ALK4 and/or ALK7 in the presence of an ActRIIligand.

In some aspects a method of blocking ActRIIA activity is provided. Infurther aspects, the method comprises contacting ActRIIA with anActRIIA-binding protein. In some instances the method is performed invivo. In other instances, the method is performed in vitro. In someaspects the blocked ActRIIA activity is selected from (a) binding by anActRIIA ligand (e.g., activin A, activin B, GDF1, GDF3, or Nodal); (b)phosphorylation of one or more Smads in cells expressing ActRIIA in thepresence of activin A; (c) phosphorylation of ALK4 and/or ALK7 in cellsexpressing ActRIIA, and ALK4 and/or ALK7 in the presence of an ActRIIAligand.

In some aspects a method of blocking ActRIIB activity is provided. Infurther aspects, the method comprises contacting ActRIIB with anActRIIB-binding protein. In some instances the method is performed invivo. In other instances, the method is performed in vitro. In someaspects the blocked ActRIIB activity is selected from (a) binding by anActRIIB ligand (e.g., activin A, activin B, GDF8 (myostatin), GDF11,BMP6, GDF3, BMP9, or BMP10); (b) phosphorylation of one or more Smads incells expressing ActRIIA in the presence of activin A; (c)phosphorylation of ALK4 and/or ALK7 in cells expressing ActRIIA, andALK4 and/or ALK7 in the presence of an ActRIIB ligand.

In one aspect, the disclosure provides for the treatment, preventionand/or amelioration of a disease or condition that comprisesadministering an ActRII-binding protein (e.g., a full-length antibodythat specifically binds ActRIIB and a full-length antibody thatspecifically binds ActRIIA) to a subject that has a disease orcondition, or is at risk of developing a disease or condition,associated with ActRII expression and/or elevated ActRII signaling. Inanother aspect the treatment includes the administration of anActRII-binding protein to an isolated tissue or cells from a subject,where the subject has a disease or condition, or is at risk ofdeveloping a disease or condition, associated with ActRII expression orActRII signaling. Further provided is use of an ActRII-binding proteinas provided herein in the manufacture of a medicament for the treatmentof a disease or condition associated with ActRII expression or ActRIIsignaling.

The disclosure provides pharmaceutical compositions comprising anActRII-binding protein and a pharmaceutically acceptable carrier. Alsoprovided are methods for treating and/or ameliorating conditionsassociated with an ActRII (e.g., ActRIIA or ActRIIB)-mediated activityin a subject, comprising administering to a subject in need thereof aneffective amount of a pharmaceutical composition comprising anActRII-binding protein provided herein. In some aspects, theActRII-binding protein is administered alone. In other aspects, theActRII-binding protein is administered as a combination therapy. Alsoprovided are methods of reducing ActRII activity in a subject comprisingadministering an effective amount of an ActRII-binding protein to asubject in need thereof.

The disclosure also provides methods for treating and/or ameliorating adisease or condition associated with a muscle disorder. In some aspects,the muscle disorder is wasting. In further aspects the wasting is due todisease or disuse. In some aspects, the method comprises administeringto a subject in need thereof, an effective amount of a pharmaceuticalcomposition comprising an ActRII-binding protein (e.g., an antibody thatspecifically binds ActRIIB an antibody that specifically binds ActRIIA,or an antibody that specifically binds ActRIIB and ActRIIA). Inadditional aspects, the ActRII-binding protein is administered alone oras a combination therapy.

According to some aspects, the disclosure provides a method of inducingthe formation of skeletal muscle in a subject. In some aspects, themethod comprises administering an ActRIIB-binding protein (e.g., ananti-ActRIIB antibody such as, a full-length ActRIIB-antibody and anActRIIB-binding antibody fragment) to a subject in need thereof. In someaspects the method increases muscle mass or strength in the subject.

The disclosure also provides methods for treating and/or ameliorating adisease or condition associated with muscle disorders such asdegenerative muscle disease, muscular dystrophy, muscle atrophy, ormuscle wasting disorders; a fibrotic condition (e.g., a hepatic,pulmonary, vascular and/or ocular fibrotic condition, such as myocardialfibrosis, and idiopathic pulmonary fibrosis (IPF)); metabolic disease(e.g., type II diabetes insulin resistance, hyperglycemia, and obesity);inflammatory disease or conditions, autoimmune disease, cardiovasculardisease (e.g., congestive heart failure, and hypertension); oculardisease such as age-related macular degeneration; pulmonary disease,musculoskeletal disease, skeletal disease such as osteoporosis;neurologic disease; wound healing; weight loss; and cancer (e.g., acarcinoma, myeloma, a bone-loss inducing cancer, pituitary cancer, andgastrointestinal cancer), in a subject. In some aspects, the methodcomprises administering to a subject in need thereof, an effectiveamount of a pharmaceutical composition comprising an ActRII-bindingprotein (e.g., an antibody that specifically binds ActRIIB, an antibodythat specifically binds ActRIIA, or an antibody that specifically bindsActRIIB and ActRIIA). In additional aspects, the ActRII-binding proteinis administered alone or as a combination therapy. Further provided isuse of disease or condition, or is at risk of developing a disease orcondition, associated with ActRII expression or ActRII signaling.

The disclosure also provides methods of reducing ActRII (e.g., ActRIIAor ActRIIB) activity such as signaling in a subject. In some aspects,the method comprises administering to a subject in need thereof (e.g., asubject diagnosed with muscle wasting; a fibrotic condition (e.g., ahepatic, pulmonary, vascular and/or ocular fibrotic condition); aninflammatory, cardiovascular, pulmonary, musculoskeletal (i.e., boneand/or muscular), neurologic, or metabolic disease or condition; woundhealing; or cancer) an effective amount of an ActRII-binding protein(e.g., an antibody that specifically binds ActRIIB, an antibody thatspecifically binds ActRIIA, or an antibody that specifically bindsActRIIB and ActRIIA) or an effective amount of a pharmaceuticalcomposition comprising an ActRII-binding protein.

In one aspect, the disclosure provides methods of treating and/orameliorating a muscle disorder in a subject. In some instances, themethod comprises administering an ActRII-binding protein (e.g., anantibody that specifically binds ActRIIB, an antibody that specificallybinds ActRIIA, or an antibody that specifically binds ActRIIB andActRIIA) to a subject having a muscle disorder. In other aspects, thesubject is at risk of developing a muscle disorder. In some aspects themuscle disorder or condition is muscle atrophy. In further aspects, themuscle atrophy is a condition associated with glucocorticoid treatmentsuch as, treatment with cortisol, dexamethasone, betamethasone,prednisone, methylprednisolone, or prednisolone. In additional aspects,the muscle atrophy is a condition associated with nerve trauma or aresult of a degenerative, metabolic, or inflammatory neuropathy (e.g.,Guillian-Barré syndrome, peripheral neuropathy, or exposure toenvironmental toxins or drugs). In additional aspects, the muscleatrophy is a condition associated with an adult motor neuron disease,infantile spinal muscular atrophy, amyotrophic lateral sclerosis,juvenile spinal muscular atrophy, autoimmune motor neuropathy withmultifocal conductor block, paralysis due to stroke or spinal cordinjury, skeletal immobilization due to trauma, prolonged bed rest,voluntary inactivity, involuntary inactivity, metabolic stress ornutritional insufficiency, cancer, AIDS, fasting, a thyroid glanddisorder, diabetes, benign congenital hypotonia, central core disease,burn injury, chronic obstructive pulmonary disease, liver diseases(examples such as fibrosis, cirrhosis), sepsis, congestive heartfailure, aging, space travel or time spent in a zero gravityenvironment.

In some aspects the treated and/or ameliorated muscle disorder is muscleatrophy associated with a myopathy. In further aspects the myopathy isselected from the group consisting of: mitochondrial myopathy; ametabolic myopathy, such as caused by a glycogen or lipid storagedisease a congenital myopathy, including nemalene myopathy,multi/minicore myopathy and myotubular (centronuclear) myopathy;myotonia; familial periodic paralysis; and inflammatory myopathy. Inadditional aspects, the myopathy is a condition associated with amuscular dystrophy syndrome, such as Duchenne, Becker, myotonic,fascioscapulohumeral, Fukuyama, limb girdle, scapulohumeral,Emery-Dreifuss, oculopharyngeal, Charcot-Marie-Tooth disease (CMT), acongenital muscular dystrophy, or hereditary distal myopathy. Theprovided ActRII-binding proteins may be used to treat inclusion bodymyositis, myoglobinurias, rhabdomyolysis, myositis ossificans,polymyositis, or dermatomyositis. In addition, the providedActRII-binding proteins may treat or prevent muscle atrophy arising fromglucocorticoid treatment, sarcopenia, prolonged bed rest, skeletalimmobilization, sepsis, or congestive heart failure

In another aspect, the disclosure provides methods of treating and/orameliorating muscular dystrophy. The term “muscular dystrophy” refers toa group of degenerative muscle diseases characterized by gradualweakening and deterioration of skeletal muscles and sometimes the heartand respiratory muscles. Exemplary muscular dystrophies that can betreated and/or ameliorated with the ActRII-binding proteins andpharmaceutical compositions provided herein include: Duchenne musculardystrophy (DMD), Becker muscular dystrophy (BMD), Emery-Dreifussmuscular dystrophy (EDMD), limb-girdle muscular dystrophy (LGMD),fascioscapulohumeral muscular dystrophy (FSH or FSHD) (also known asLandouzy-Dejerine), myotonic muscular dystrophy (MMD) (also known asSteinert's Disease), oculopharyngeal muscular dystrophy (OPMD), distalmuscular dystrophy (DD), congenital muscular dystrophy (CMD), andscapulohumeral muscular dystrophy (SMD).

In another aspect, the disclosure provides methods of treating and/orameliorating a fibrotic condition (e.g., a fibrosis). In some instances,the method comprises administering an ActRII-binding protein (e.g., anantibody that specifically binds ActRIIB, an antibody that specificallybinds ActRIIA, or an antibody that specifically binds ActRIIB andActRIIA) to a subject having a fibrotic condition. In other aspects, thesubject is at risk of developing a fibrotic condition. In furtheraspects the fibrotic condition is DN. In some aspects, the treatedfibrotic condition is a primary fibrosis. In one aspect, the treatedfibrotic condition is idiopathic. In some aspects the fibrotic conditionis chronic. In some aspects, the treated fibrotic condition is systemic.In other aspects, the treated fibrotic disease or condition is acondition associated with (e.g., is secondary to) a disease (e.g., aninfectious disease, an inflammatory disease, an autoimmune disease, amalignant or cancerous disease, and/or a connective disease); a toxin;an insult (e.g., an environmental hazard (e.g., asbestos, coal dust,polycyclic aromatic hydrocarbons), cigarette smoking, a wound); or amedical treatment (e.g., surgical incision, chemotherapy or radiation).

Fibrotic conditions that can be treated and/or ameliorated with theActRII-binding proteins provided herein include, but are not limited to,fibrosis, hepatic injury (e.g., liver injury caused by alcohol, andviral infection such as, Hepatitis B and C infection), pulmonaryfibrosis (e.g., cystic fibrosis, IPF or lung fibrosis caused bycigarette smoking, environmental hazards and chemotherapeutic drugs suchas, bleomycin), radiation induced fibrosis, injection fibrosis, vascularfibrosis, atherosclerosis, pancreatic fibrosis, musculoskeletal fibrosis(e.g., muscle fibrosis), cardiac fibrosis, skin fibrosis, scleroderma,ophthalmic fibrosis (e.g., age-related macular degeneration, diabeticmacular edema, diabetic retinopathy, and dry eye disease), progressivesystemic sclerosis (PSS), chronic graft-versus-host disease, Peyronie'sdisease, post-cystoscopic urethral stenosis, retroperitoneal fibrosis,mediastinal fibrosis, progressive massive fibrosis, proliferativefibrosis, neoplastic fibrosis, Dupuytren's disease, strictures, pleuralfibrosis, sarcoidosis, spinal cord injury/fibrosis, and myelofibrosis.

Also provided are methods of decreasing fibrosis in a subject. In someaspects, the disclosure provides a method of decreasing fibrosis in asubject that comprises administering an ActRII-binding protein (e.g., ina pharmaceutical composition described herein) to a subject having afibrosis. Such decreased fibrosis can be reflected in for example,reduced fibrosis and decreases signs or conditions associated withfibrosis including for example, decreased development of fibroticlesions, a decrease in weight loss or other clinical symptoms, and/or analtered expression of biological molecules (e.g., mRNA or proteinexpression) associated with development of the fibrotic condition beingtreated. In some aspects, the fibrosis is a hepatic, muscle, orpulmonary fibrosis. Further provided is use of an ActRII-binding proteinas provided herein in the manufacture of a medicament for the treatmentof fibrosis.

In another aspect, the disclosure provides methods of reducing fibrosisin cells or tissues. The methods include contacting a fibrotic cell ortissue with an ActRII-binding protein (e.g., as a single agent or incombination with another agent or therapeutic modality) in an amountsufficient to decrease or inhibit the fibrosis. These methods can becarried out in vitro or in vivo. In one aspect, the method is carriedout in vivo, for example, in a mammalian subject (e.g., an animalmodel). In one aspect the subject is a human. In some aspects, reducingfibrosis includes: (a) reducing or inhibiting the formation ordeposition of tissue fibrosis; (b) reducing the size, cellularity (e.g.,fibroblast or immune cell numbers), composition; or cellular content, ofa fibrotic lesion; (c) reducing the collagen or hydroxyproline content,of a fibrotic lesion; (d) reducing expression or activity of one or morefibrogenic proteins; and/or (e) reducing fibrosis associated with aninflammatory response. In some aspects, reducing fibrosis includes: (a)reducing or inhibiting the formation or deposition of tissue fibrosis;(b) reducing the size, cellularity (e.g., fibroblast or immune cellnumbers), composition; or cellular content, of a fibrotic lesion; (c)reducing the collagen or hydroxyproline content, of a fibrotic lesion;(d) reducing expression or activity of one or more fibrogenic proteins;and/or (e) reducing fibrosis associated with inflammation.

According to some aspects, the disclosure provides methods of reducingthe loss of hepatic or pulmonary function in a subject. In some aspects,the method comprises administering an ActRII-binding protein (e.g., ananti-ActRII antibody such as, a full-length ActRII-antibody and anActRII-binding antibody fragment) to a subject in need thereof. In someaspects the method reduces the loss of hepatic function in a subject. Infurther aspects, the method reduces the loss of hepatic function in asubject through reducing hepatic fibrosis. In some aspects the methodreduces the loss of pulmonary function in a subject. In some aspects themethod reduces the loss of pulmonary function in a subject throughreducing pulmonary fibrosis. In some aspects the methods reduces theloss of pulmonary function and/or pulmonary fibrosis in a subject havingor at risk of developing idiopathic pulmonary fibrosis (IPF).

Additionally provided are methods of improving hepatic or pulmonaryfunction by reducing fibrosis in a subject. In some instances, themethod comprises administering an ActRII-binding protein e.g., ananti-ActRII antibody such as, a full-length ActRII-antibody and anActRII-binding antibody fragment, and variants and derivatives thereof)or pharmaceutical composition provided herein to a subject in needthereof. In some aspects, reducing the loss of, or improving, hepatic orpulmonary function includes: (a) reducing or inhibiting the formation ordeposition of tissue fibrosis in the corresponding organ; (b) reducingthe size, cellularity (e.g., fibroblast or immune cell numbers),composition; or cellular content, of a fibrotic lesion in thecorresponding organ; (c) reducing the collagen or hydroxyprolinecontent, of a fibrotic lesion in the corresponding organ; (d) reducingexpression or activity of one or more fibrogenic proteins (e.g.,fibrinogen and collagen) in the corresponding organ; (d) reducingexpression extracellular matrix and/or EMT in the corresponding organ;and/or (e) reducing fibrosis associated with an inflammatory response inthe corresponding organ.

The human body responds to trauma and injury by scarring. Fibrosis, atype of disorder characterized by excessive scarring, occurs when thenormal wound healing response is disturbed. During fibrosis, the woundhealing response continues causing an excessive production anddeposition of collagen. In another aspect, the disclosure provides amethod for treating fibrosis comprising administering to a subject inneed thereof a therapeutically effective amount of ActRII-bindingprotein (e.g., an antibody that specifically binds ActRIIB or anantibody that specifically binds ActRIIA).

In some aspects, the disclosure provides methods of reducing the lossof, or improving, hepatic or pulmonary function. In some aspects, themethod results in: (a) reducing or inhibiting the formation ordeposition of tissue fibrosis in the corresponding organ; (b) reducingthe size, cellularity (e.g., fibroblast or immune cell numbers),composition; or cellular content, of a fibrotic lesion in thecorresponding organ; (c) reducing the collagen or hydroxyprolinecontent, of a fibrotic lesion in the corresponding organ; (d) reducingexpression or activity of one or more fibrogenic proteins (e.g.,fibrinogen and collagen) in the corresponding organ; (d) reducingexpression extracellular matrix and/or EMT in the corresponding organ;and/or (e) reducing fibrosis associated with an inflammatory response inthe corresponding organ.

The disclosure also provides methods of treating and/or ameliorating afibrotic condition of the lung. In some aspects, the method comprisesadministering an ActRII-binding protein (e.g., an anti-ActRII antibodysuch as, an antibody that specifically binds ActRII, and fragments andvariants and derivatives thereof) to a subject having or at risk ofdeveloping, a fibrotic condition of the lung. In some aspects, thepulmonary fibrosis is idiopathic, pharmacologically-induced,radiation-induced, chronic obstructive pulmonary disease (COPD), orchronic asthma. Fibrotic conditions of the lung that can be treatedinclude one or more members of the group consisting of: usualinterstitial pneumonitis (UIP), interstitial lung disease, cryptogenicfibrosing alveolitis (CFA), and bronchiectasis. In some aspects thetreated fibrotic condition of the lung is a condition associated with aninflammatory disorder of the lung, e.g., asthma, and/or chronicobstructive pulmonary disease (COPD).

In particular aspects, the disclosure provides a method of treatingand/or ameliorating a pulmonary fibrosis that comprises administering anActRII-binding protein to a subject having or at risk of developing,pulmonary fibrosis. Further provided is use of an ActRII-binding proteinas provided herein in the manufacture of a medicament for the treatmentor amelioration of pulmonary fibrosis.

In some aspects, the fibrotic condition of the lung treated with anActRII-binding protein (e.g., and anti-ActRIIA antibody and ananti-ActRIIB antibody) is a member selected from the group consistingof: acute respiratory distress syndrome, chronic asthma, acute lungsyndrome, bronchopulmonary dysplasia, pulmonary hypertension (e.g.,idiopathic pulmonary hypertension (IPH)), histiocytosis Xpneumoconiosis, Caplan's disease, rheumatoid disease, and systemicsclerosis.

In some aspects, the fibrotic condition of the lung treated with anActRII-binding protein (e.g., and anti-ActRIIA antibody and ananti-ActRIIB antibody) provided herein is a condition associated with anautoimmune connective tissue disorder. In some aspects, the autoimmuneconnective tissue disorder is selected from the group consisting of:sarcoidosis rheumatoid arthritis, scleroderma and systemic lupuserythematosus (SLE). In additional aspects, the fibrotic condition ofthe lung is a condition associated with a disease, a toxin, an insult,or a medical treatment. Thus, in some aspects, the fibrotic condition ofthe lung is a condition associated with one or more members of the groupconsisting of: exposure to toxins and irritants including, inhaledworkplace hazards (e.g., dust, asbestos, silica, bauxite, iron, cotton,talc, and coal dust), toxins (e.g., amiodarone, carmustine,chloramphenicol, hexamethonium), cigarette smoke, and environmentalpollutants. In additional aspects, the treated fibrotic condition of thelung is a condition associated with an infectious disease. In particularaspects the infectious disease is a condition associated with a chronicinfection.

In additional aspects, the treated fibrotic condition of the lung is acondition associated with a medical treatment. In particular aspects themedical treatment is selected from surgery, radiation therapy, and drugtherapy. In further aspects, the drug therapy is chemotherapy. Infurther aspects, the chemotherapy involves the administration of achemotherapeutic agent selected from the group consisting of bleomycin,methotrexate, amiodarone, busulfan, nitrosourea, and nitrofurantoin.

Also provided are methods of treating and/or ameliorating pulmonaryhypertension or idiopathic pulmonary fibrosis (IPF). In some instances,the method comprises administering an ActRII-binding protein (e.g., ananti-ActRII antibody such as, a full-length ActRII-antibody and anActRII-binding antibody fragment, and variants and derivatives thereof)to a subject having or at risk of developing pulmonary hypertension orIPF. In some instances, the ActRII-binding protein or the pharmaceuticalcomposition comprising an ActRII-binding-protein is administered totreat prevent, and/or ameliorate pulmonary hypertension. In someinstances, the ActRII-binding protein or the pharmaceutical compositioncomprising an ActRII-binding protein is administered to treat, prevent,and/or ameliorate IPF. In some aspects, the ActRII-binding protein orthe pharmaceutical composition comprising an ActRII-binding protein isadministered to a subject having or at risk of developing pulmonaryhypertension or IPF.

The disclosure also provides methods of treating and/or amelioratingfibrotic condition of the liver. In some aspects, the method comprisesadministering an ActRII-binding protein or an effective amount of apharmaceutical composition comprising an ActRII-binding protein to asubject having or at risk of developing, a fibrotic condition of theliver. Further provided is use of an ActRII-binding protein as providedherein in the manufacture of a medicament for the treatment oramelioration of a fibrotic condition of the liver. Fibrotic conditionsof the liver that can be treated using ActRII-binding proteins providedherein include one or more members of the group consisting of: steatosis(e.g., nonalcoholic steatohepatitis (NASH), fatty liver disease,cholestatic liver disease (e.g., primary biliary cirrhosis (PBC)), livercirrhosis, alcohol induced liver fibrosis, infection-induced liverfibrosis, biliary duct injury, biliary fibrosis, congenital hepaticfibrosis, autoimmune hepatitis, and a cholangiopathy. In furtheraspects, the infection-induced liver fibrosis is bacterial-induced orviral-induced.

In an additional aspect, the fibrotic condition of the liver that can betreated with an ActRII-binding protein provided herein is one or moremembers of the group consisting of: hepatic fibrosis associated withviral infection (e.g., hepatitis (hepatitis C, B and D), autoimmunehepatitis, non-alcoholic fatty liver disease (NAFLD), progressivemassive fibrosis, alcoholism, and exposure to toxins or irritants (e.g.,alcohol, pharmaceutical drugs and environmental toxins).

The disclosure also provides methods of treating and/or amelioratingcardiac fibrosis. In some aspects, the method comprises administering anActRII-binding protein or an effective amount of a pharmaceuticalcomposition comprising an ActRII-binding protein to a subject having orat risk of developing, a fibrotic condition of the cardiovascularsystem. In some embodiments, the cardiac fibrosis is endomyocardialfibrosis or idiopathic myocardiopathy. In some embodiments, the skinfibrosis is scleroderma, post-traumatic, operative cutaneous scarring,keloids, or cutaneous keloid formation. In some embodiments, the eyefibrosis is glaucoma, sclerosis of the eyes, conjunctival scarring,corneal scarring, or pterygium. In some embodiments, the retroperitonealfibrosis is idiopathic, pharmacologically-induced or radiation-induced.In some embodiments, the cystic fibrosis is cystic fibrosis of thepancreas or cystic fibrosis of the lungs. In some embodiments, theinjection fibrosis occurs as a complication of an intramuscularinjection. Further provided is use of an ActRII-binding protein asprovided herein in the manufacture of a medicament for the treatment oramelioration of a fibrotic condition of the fibrotic condition of thecardiovascular system.

Also provided are methods of treating and/or ameliorating an oculardisease or condition comprising administering an ActRII-binding proteinto a subject in need thereof. In particular aspects the ocular diseaseor condition is glaucoma. In some aspects, the ocular disease isretinopathy. In further aspects, the ocular disease is diabeticretinopathy.

In additional aspects, the disclosure provides methods of treatingand/or ameliorating a fibrotic condition of the eye (e.g., fibrosis ofthe eye, ophthalmic fibroses, and fibrosis associated with retinaldysfunction). Thus, in some instances, the method comprisesadministering an ActRII-binding protein to a subject having or at riskfor developing a fibrotic condition of the eye. Further provided is useof an ActRII-binding protein as provided herein in the manufacture of amedicament for the treatment or amelioration of a fibrotic condition ofthe fibrotic condition of the cardiovascular system.

Fibrotic conditions of the eye that can be treated according to themethods provided herein can occur in response to injury, such asmechanical wound (e.g., fibrosis associated with alkali burn) or variousmetabolic malfunctions (including, e.g., responses to inflammation,ischemia, and degenerative disease). In some aspects, the disclosureprovides methods for treating fibrosis associated with ocular surgery.In further aspects, the fibrosis is a condition associated withpostoperative scarring in an ocular condition. In further aspects, thepostoperative scarring is a condition associated with surgery involving,retinal reattachment, cataract extraction or a drainage procedure.

In some aspects, the disclosure provides a method of treating and/orameliorating a fibrotic condition of the eye associated with one or moremembers of the group consisting of: macular edema (e.g., diabeticmacular edema), dry eye disease, fibrosis of the lens, fibrosis of thecorneal stroma or endothelium, scarring in the cornea and conjunctiva,fibrovascular scarring, retinal fibrosis, and retinal gliosis.

In some aspects, the disclosure provides a method for treating afibrotic condition of the eye associated with macular degeneration. Insome embodiments, the treated fibrotic condition is a conditionassociated with age-related macular degeneration. In some embodimentsthe treated condition is a condition associated with wet maculardegeneration. In other embodiments the treated condition is a conditionassociated with dry macular degeneration.

In some aspects, the disclosure provides a method for treating and/orameliorating an inflammatory disease or condition that comprisesadministering an ActRII-binding protein to a subject in need thereof.Further provided is use of an ActRII-binding protein as provided hereinin the manufacture of a medicament for the treatment or amelioration ofinflammatory disease or condition. In some aspects, the inflammatorydisease or condition is inflammatory cancer, inflammation associatedwith fibrosis, inflammation associated with atherosclerosis, asthma oran autoimmune disorder.

Additionally provided are methods of treating and/or ameliorating acardiovascular disease or condition. Further provided is use of anActRII-binding protein as provided herein in the manufacture of amedicament for the treatment or amelioration of a cardiovascular diseaseor condition. In some instances, the method comprises treating orameliorating a cardiovascular disease or condition by administering anActRII-binding protein to a subject in need thereof. In some aspects,the cardiovascular disease or condition is anemia, congestive heartfailure, ventricular dysfunction, vascular calcification, pulmonaryhypertension, arterial restenosis, or myocardial fibrosis.

In some aspects, the disclosure provides a method for treating and/orameliorating a pulmonary disease or condition that comprisesadministering an ActRII-binding protein to a subject in need thereof.Further provided is use of an ActRII-binding protein as provided hereinin the manufacture of a medicament for the treatment or amelioration ofa pulmonary disease or condition.

In some aspects, the disclosure provides a method for treating and/orameliorating a musculoskeletal disease or condition that comprisesadministering an effective dose of ActRII-binding protein to a subjectin need thereof. Further provided is use of an ActRII-binding protein asprovided herein in the manufacture of a medicament for the treatment oramelioration of a musculoskeletal disease or condition. ExemplaryActRIIB-associated conditions that can be treated and/or ameliorated byadministering an effective dose of an ActRII-binding protein (e.g.,anti-ActRIIB antibody) include neuromuscular disorders (e.g., musculardystrophy and muscle atrophy), congestive obstructive pulmonary diseaseor pulmonary emphysema (and associated muscle wasting), muscle wastingsyndrome, sarcopenia, cachexia, adipose tissue disorders (e.g.,obesity), type 2 diabetes, and bone degenerative disease (e.g.,osteoporosis). The use of an ActRII-binding protein as provided hereinin the manufacture of a medicament for the treatment or amelioration ofeach of these diseases or conditions is provided herein.

Other exemplary ActRII-associated conditions that can be treated and/orameliorated by administering an effective dose of an ActRII-bindingprotein (e.g., anti-ActRIIB antibody) include musculodegenerative andneuromuscular disorders, and osteoporosis.

The provided ActRII-binding proteins provide an effective means toincrease muscle mass in other neuromuscular diseases or conditions thatare in need of muscle growth. For example, in amyotrophic lateralsclerosis (ALS). Other neuromuscular diseases in which ActRII-bindingproteins may be useful include paralysis due to spinal cord injury orstroke; denervation due to trauma or degenerative, metabolic, orinflammatory neuropathy; adult motor neuron disease; autoimmune motorneuropathy with multifocal conductor block; and infantile or juvenilespinal muscular atrophy.

In other aspects, the disclosure provides methods of inducing boneand/or cartilage formation, preventing bone loss, increasing bonemineralization or preventing the demineralization of bone. For example,the provided ActRII-binding proteins have use in treating osteoporosisand the healing of bone fractures and cartilage defects in a subject(e.g., humans and other animals). In some aspects, the disclosureprovides a method for healing bone fractures or cartilage in a subject.In another aspect, the provided methods and compositions areadministered to treat a condition causing bone loss such asosteoporosis, hyperparathyroidism, Cushing's disease, thyrotoxicosis,chronic diarrheal state or malabsorption, or anorexia nervosa.

In additional aspects, the disclosure provides a method for treating aneurological disorder or condition that comprises administering anActRII-binding protein to a subject in need thereof. Further provided isuse of an ActRII-binding protein as provided herein in the manufactureof a medicament for the treatment or amelioration of a neurologicaldisorder or condition. In some aspects, the neurological disorder orcondition is associated with neuronal death. In some aspects, theneurological disorder or condition is Parkinson's Disease, ALS; brainatrophy, or dementia.

In additional aspects, the disclosure provides a method for treating ametabolic disorder or condition that comprises administering anActRII-binding protein to a subject in need thereof. Further provided isuse of an ActRII-binding protein as provided herein in the manufactureof a medicament for the treatment or amelioration of a metabolicdisorder or condition. In some aspects, the metabolic disorder orcondition is a condition associated with diabetes. In some aspects themetabolic disorder or condition is obesity. In further aspects themetabolic disorder or condition is hypertrophic obesity. In someaspects, the metabolic disorder or condition is cancer cachexia ormuscle wasting.

In other aspects, the disclosure provides positions and methods forregulating body fat content in a subject and for treating or preventingconditions related thereto, and particularly, health-compromisingconditions related thereto.

As provided herein, to regulate (control) body weight can refer toreducing or increasing body weight, reducing or increasing the rate ofweight gain, or increasing or reducing the rate of weight loss, and alsoincludes actively maintaining, or not significantly changing body weight(e.g., against external or internal influences which may otherwiseincrease or decrease body weight). According to one aspect, thedisclosure provides a method of regulating body weight by administeringto a subject (e.g., a human) in need thereof an ActRII-binding proteinprovided herein. In one aspect, the disclosure provides a method forreducing body weight and/or reducing weight gain in an subject, and moreparticularly, for treating or ameliorating obesity in a patient at riskfor or suffering from obesity. In another aspect, the disclosureprovides a method and compounds for treating a subject that is unable togain or retain weight (e.g., an animal with a wasting syndrome). Suchmethods are effective to increase body weight and/or mass, or to reduceweight and/or mass loss, or to improve conditions associated with orcaused by undesirably low (e.g., unhealthy) body weight and/or mass. Theprovided ActRIIB-binding proteins may further be used as a therapeuticagent for slowing or preventing the development of type II diabetes andmetabolic syndrome.

In particular aspects, the disclosure provides a method of treatingand/or ameliorating a condition associated with diabetes that comprisesadministering an ActRII-binding protein to a subject having or at riskof developing, diabetes and/or a condition associated with diabetes.Further provided is use of an ActRII-binding protein as provided hereinin the manufacture of a medicament for the treatment or amelioration ofdiabetes or a condition associated with diabetes. In one aspect, thecondition associated with diabetes is diabetic neuropathy, diabeticretinopathy, diabetic nephropathy, diabetic vasculopathy or diabeticmicroangiopathy.

In additional aspects, the disclosure provides a method for promotingwound healing that comprises administering an ActRII-binding protein toa subject in need thereof. In some aspects the ActRII-binding protein isadministered to a subject to reduce scar formation associated with woundhealing. In some aspects the ActRII-binding protein is administered to asubject at risk of developing a hypertrophic scar or keloid.

Additionally provided are methods of antagonizing ActRII activity in apathological condition associated with ActRII expression and/or ActRIIsignaling. In some instances, the method comprises administering anActRII-binding protein (e.g., an anti-ActRII antibody such as, afull-length anti-ActRII-antibody or an ActRII-binding antibody fragment)to a subject in need thereof. In some aspects the pathological conditionis a musculoskeletal disease or disorder, such as muscle atrophy. Insome aspects the pathological condition is a fibrotic disease of, forexample, the lung or liver. In further aspects, the pathologicalcondition is diabetes. In some aspects, the pathological condition isobesity (e.g., hypertrophic obesity). In additional aspects, thepathological condition is pulmonary hypertension or idiopathic pulmonaryfibrosis (IPF). In some aspects the pathological condition is an oculardisease such as, diabetic retinopathy. In some aspects the pathologicalcondition is a cancer, such as a carcinoma (e.g., basal and squamouscell carcinomas of the skin, head and neck carcinomas, and renal cellcarcinoma), myeloma (e.g., multiple myeloma), colorectal cancer, or abone-loss inducing cancer.

Methods of antagonizing ActRIIB activity in a pathological conditionassociated with ActRIIB expression and/or increased ActRIIB signalingare also provided. In some instances, the method comprises administeringan ActRII-binding protein (e.g., an anti-ActRII antibody such as, afull-length anti-ActRIIB-antibody and an ActRIIB-binding antibodyfragment, and variants and derivatives thereof) to a subject in needthereof. In some aspects the pathological condition is a musculoskeletaldisease or disorder, such as muscle atrophy. In some aspects thepathological condition is a fibrotic disease of, for example, the lungor liver. In further aspects, the pathological condition is diabetes. Insome aspects, the pathological condition is obesity (e.g., hypertrophicobesity). In additional aspects, the pathological condition is pulmonaryhypertension or idiopathic pulmonary fibrosis (IPF). In some aspects thepathological condition is an ocular disease such as, diabeticretinopathy. In some aspects the pathological condition is a cancer,such as a carcinoma (e.g., basal and squamous cell carcinomas of theskin, and head and neck carcinomas), myeloma, renal cell carcinoma,colorectal cancer, or a bone-loss inducing cancer.

Additionally provided are methods of antagonizing ActRIIA activity in apathological condition associated with ActRIIA expression and/orincreased ActRIIA signaling. In some instances, the method comprisesadministering an ActRII-binding protein (e.g., an anti-ActRII antibodysuch as, a full-length anti-ActRIIA-antibody or an ActRIIA-bindingantibody fragment) to a subject in need thereof. In some aspects thepathological condition is a musculoskeletal disease or disorder, such asmuscle atrophy. In one aspect the pathological condition is a fibroticdisease. In some aspects the pathological condition is a fibroticdisease of, for example, the lung or liver. In a further aspect thepathological condition is a fibrotic disease of lung or liver. Infurther aspects, the pathological condition is diabetes. In someaspects, the pathological condition is obesity (e.g., hypertrophicobesity). In additional aspects, the pathological condition is pulmonaryhypertension or idiopathic pulmonary fibrosis (IPF). In some aspects thepathological condition is an ocular disease such as, diabeticretinopathy. In some aspects the pathological condition is a cancer,such as a carcinoma (e.g., basal and squamous cell carcinomas of theskin, head and neck carcinomas), myeloma (e.g., multiple myeloma),colorectal cancer, or a bone-loss inducing cancer.

Additionally provided are methods of antagonizing ActRIIB and ActRIIAactivity in a pathological condition associated with ActRIIB and/orActRIIA expression, and/or increased ActRIIB and/or ActRIIA signaling.In some instances, the method comprises administering an ActRII-bindingprotein (e.g., an anti-ActRII antibody such as, a full-lengthanti-ActRII-antibody or an ActRII-binding antibody fragment) to asubject in need thereof. In some aspects the pathological condition is amusculoskeletal disease or disorder, such as muscle atrophy. In oneaspect the pathological condition is a fibrotic disease. In some aspectsthe pathological condition is a fibrotic disease of, for example, thelung, or liver. In a further aspect the pathological condition is afibrotic disease of the lung, or liver. In further aspects, thepathological condition is diabetes. In some aspects, the pathologicalcondition is obesity (e.g., hypertrophic obesity). In additionalaspects, the pathological condition is pulmonary hypertension oridiopathic pulmonary fibrosis (IPF). In some aspects the pathologicalcondition is an ocular disease such as, diabetic retinopathy. In someaspects the pathological condition is a cancer, such as a carcinoma(e.g., basal and squamous cell carcinomas of the skin, head and neckcarcinomas), myeloma (e.g., multiple myeloma), colorectal cancer, or abone-loss inducing cancer.

In additional aspects, the disclosure provides methods of treatingand/or ameliorating cancer or a condition associated with cancer or thetreatment thereof, that comprises administering an ActRII-bindingprotein (e.g., an anti-ActRII antibody or ActRII-binding fragmentthereof) to a subject in need thereof. In some aspects theActRII-binding protein is an anti-ActRIIB antibody or an ActRIIB-bindingfragment thereof. Further provided is use of an ActRII-binding proteinas provided herein in the manufacture of a medicament for the treatmentor amelioration of cancer or a condition associated with cancer. In someaspects the ActRII-binding protein is an anti-ActRIIA antibody or anActRIIA-binding fragment thereof. In some aspects the ActRII-bindingprotein is an antibody that binds ActRIIB and ActRIIA or an ActRIIB andActRIIA ActRIIB-binding fragment thereof. In some aspects, the subjecthas a cancer selected from the group consisting of a: melanoma, uterinecancer, lung cancer, ovarian cancer, breast cancer, colon cancer,pancreatic cancer and a sarcoma. In particular aspects, the subject hasa carcinoma (e.g., basal and squamous cell carcinomas of the skin, andhead and neck carcinoma), myeloma, colorectal cancer, or a bone-lossinducing cancer.

In some aspects, the method comprises contacting a cancer cell, tumorassociated-stromal cell, or endothelial cell expressing ActRII (e.g.,ActRIIB and/or ActRIIA), with an ActRII-binding protein thatspecifically binds the ActRII. In some instances, the method comprisescontacting activin A with an ActRII-binding protein. In additionalaspects the tumor cell is from a cancer selected from the groupconsisting of: myelofibrosis, myeloma (e.g., multiple myeloma),pituitary cancer. In another aspect, the cancer is breast cancer,gastrointestinal cancer, or a carcinoma (e.g., basal and squamous cellcarcinomas). In an additional aspect, the cancer is a bone-loss-inducingcancer. In some aspects the tumor cell is from a cancer line.

The disclosure provides methods that comprise administering atherapeutically effective amount of a ActRII-binding protein, alone orin combination with one or more additional therapies (e.g., one or moreadditional therapeutic agents) to a subject having, or at risk fordeveloping, a fibrotic condition. The disclosure additionally providescompositions for use of an ActRII-binding protein alone or incombination with another agent for preparation of one or moremedicaments for use in treating (e.g., preventing), and/or amelioratinga ActRII-mediated disease and/or condition (e.g., muscle disorders suchas degenerative muscle disease, muscular dystrophy, muscle atrophy, ormuscle wasting disorders; a fibrotic condition (e.g., a hepatic,pulmonary, vascular and/or ocular fibrotic condition, such as myocardialfibrosis, and idiopathic pulmonary fibrosis (IPF)); metabolic disease(e.g., type II diabetes insulin resistance, hyperglycemia, and obesity);inflammatory disease or conditions, autoimmune disease, cardiovasculardisease (e.g., congestive heart failure, and hypertension); oculardisease such as age-related macular degeneration; pulmonary disease,musculoskeletal disease, skeletal disease such as osteoporosis;neurologic disease; wound healing; weight loss; and cancer (e.g., acarcinoma, myeloma, a bone-loss inducing cancer, pituitary cancer, andgastrointestinal cancer)).

Also provided is the use of an ActRII-binding protein provided hereinfor diagnostic monitoring of protein levels (e.g., ActRIIB and/orActRIIA levels) in blood or tissue as part of a clinical testingprocedure, e.g., to determine the efficacy of a given treatment regimen.For example, detection can be facilitated by coupling an ActRII-bindingprotein to a detectable substance. Examples of detectable substancesinclude various enzymes, prosthetic groups, fluorescent materials,luminescent materials, bioluminescent materials, and radioactivematerials. Examples of suitable enzymes include horseradish peroxidase,alkaline phosphatase, β-galactosidase, or acetylcholinesterase; examplesof suitable prosthetic group complexes include streptavidin/biotin andavidin/biotin; examples of suitable fluorescent materials includeumbelliferone, fluorescein, fluorescein isothiocyanate, rhodamine,dichlorotriazinylamine fluorescein, dansyl chloride or phycoerythrin; anexample of a luminescent material includes luminol; examples ofbioluminescent materials include luciferase, luciferin, and acquorin;and examples of suitable radioactive material include ¹²⁵I, ¹³¹I, ³⁵S,or ³H.

Pharmaceutical Compositions and Administration Methods

Methods of preparing and administering an ActRII-binding protein to asubject in need thereof are known to or are readily determined by thoseof ordinary skill in the art. The route of administration of theActRII-binding proteins can be, for example, oral, parenteral, byinhalation or topical. The term parenteral includes, e.g., intravenous,intraarterial, intraperitoneal, intramuscular, intraocular,subcutaneous, rectal, or vaginal administration. While all these formsof administration are clearly contemplated as being within the scope ofthe disclosure, another example of a form for administration would be asolution for injection, in particular for intravenous or intraarterialinjection or drip. Usually, a suitable pharmaceutical composition cancomprise a buffer (e.g., acetate, phosphate or citrate buffer), asurfactant (e.g., polysorbate), optionally a stabilizer agent (e.g.,human albumin), etc. In other methods compatible with the teachingsherein, ActRII-binding proteins as provided herein can be delivereddirectly to the organ and/or site of a fibrosis or tumor, therebyincreasing the exposure of the diseased tissue to therapeutic agent. Inone aspect, the administration is directly to the airway, e.g., byinhalation or intranasal administration.

As discussed herein, ActRII-binding proteins can be administered in apharmaceutically effective amount for the in vivo treatment ofActRII-mediated diseases and conditions including but not limited to,muscle disorders such as degenerative muscle disease, musculardystrophy, muscle atrophy, or muscle wasting disorders; a fibroticcondition (e.g., a hepatic, pulmonary, vascular and/or ocular fibroticcondition, such as myocardial fibrosis, and idiopathic pulmonaryfibrosis (IPF)); metabolic disease (e.g., type II diabetes insulinresistance, hyperglycemia, and obesity); inflammatory disease orconditions, autoimmune disease, cardiovascular disease (e.g., congestiveheart failure, and hypertension); ocular disease such as age-relatedmacular degeneration; pulmonary disease, musculoskeletal disease,skeletal disease such as osteoporosis; neurologic disease; woundhealing; weight loss; and cancer (e.g., a carcinoma, myeloma, abone-loss inducing cancer, pituitary cancer, and gastrointestinalcancer. In this regard, it will be appreciated that the disclosedActRII-binding proteins can be formulated so as to facilitateadministration and promote stability of the active agent. Pharmaceuticalcompositions in accordance with the disclosure can comprise apharmaceutically acceptable, non-toxic, sterile carrier such asphysiological saline, non-toxic buffers, preservatives and the like. Forthe purposes of the instant application, a pharmaceutically effectiveamount of a ActRII-binding protein, conjugated or unconjugated, means anamount sufficient to achieve effective binding to ActRII and to achievea benefit, e.g., to ameliorate symptoms of a disease or condition or todetect a substance or a cell. Suitable formulations for use intherapeutic methods disclosed herein are described in Remington'sPharmaceutical Sciences (Mack Publishing Co.) 16th ed. (1980).

Certain pharmaceutical compositions provided herein can be orallyadministered in an acceptable dosage form including, e.g., capsules,tablets, aqueous suspensions or solutions. Certain pharmaceuticalcompositions also can be administered by nasal aerosol or inhalation.Such compositions can be prepared as solutions in saline, employingbenzyl alcohol or other suitable preservatives, absorption promoters toenhance bioavailability, and/or other conventional solubilizing ordispersing agents.

The amount of an ActRII-binding protein (e.g., an antibody thatspecifically binds ActRIIB and/or ActRIIA) that can be combined withcarrier materials to produce a single dosage form will vary dependingupon the subject treated and the particular mode of administration. Thecomposition can be administered as a single dose, multiple doses or overan established period of time in an infusion. Dosage regimens also canbe adjusted to provide the optimum desired response (e.g., a therapeuticor prophylactic response).

ActRII-binding proteins provided herein can be administered to a humanor other subject in accordance with the aforementioned methods oftreatment in an amount sufficient to produce a therapeutic effect. TheActRII-binding proteins provided herein can be administered to suchhuman or other animal in a conventional dosage form prepared bycombining the ActRII-binding proteins with a conventionalpharmaceutically acceptable carrier or diluent according to knowntechniques. The form and character of the pharmaceutically acceptablecarrier or diluent can be dictated by the amount of active ingredientwith which it is to be combined, the route of administration and otherwell-known variables. A cocktail comprising one or more differentActRII-binding proteins can also be used.

Therapeutically effective doses of ActRII-binding compositions fortreatment of an ActRII-mediated disease or condition such asdegenerative muscle disease, muscular dystrophy, muscle atrophy, ormuscle wasting disorders; a fibrotic condition; an inflammatory,autoimmune, cardiovascular, pulmonary, musculoskeletal, skeletal,ocular, neurologic, or metabolic disease or condition; obesity; woundhealing; and cancer, vary depending upon many different factors,including means of administration, target site, physiological state ofthe subject, whether the subject is human or an animal, othermedications administered, and whether treatment is prophylactic ortherapeutic. Usually, the subject is a human, but non-human mammalsincluding transgenic mammals can also be treated. Treatment dosages canbe titrated using routine methods known to those of ordinary skill inthe art to optimize safety and efficacy.

To ameliorate the symptoms of a particular disease or condition byadministration of an ActRII-binding protein refers to any lessening,whether permanent or temporary, lasting or transient that can beattributed to or associated with administration of the ActRII-binding.

The disclosure also provides for the use of an ActRII-binding protein,such as, an anti-ActRII antibody in the manufacture of a medicament forexample, for treating or degenerative muscle disease, musculardystrophy, muscle atrophy, or muscle wasting disorders; a fibroticcondition; an inflammatory, autoimmune, cardiovascular, pulmonary,musculoskeletal, skeletal, ocular, neurologic, or metabolic disease orcondition; obesity; wound healing; and cancer.

Combination Therapies

In some aspects, an ActRII-binding protein (e.g., an anti-ActRIIantibody such as, a full-length ActRII-antibody and an ActRII-bindingantibody fragment, and variants and derivatives thereof) is administeredin combination with one or more other therapies. Such therapies includeadditional therapeutic agents as well as other medical interventions.Exemplary therapeutic agents that can be administered in combinationwith the ActRII-binding proteins provided herein include, but are notlimited to, anti-SDI-fibrotics, corticosteroids, anti-inflammatories,angiotensin converting enzyme inhibitors, angiotensin receptor blockers,diuretics, antidiabetics, immune suppressants, chemotherapeutic agents,anti-metabolites, and immunomodulators. In various aspects, anActRII-binding protein is administered to a subject before, during,and/or after a surgical excision/removal procedure.

Diagnostics

The disclosure also provides a diagnostic method useful during diagnosisof ActRII-mediated diseases and conditions (e.g., muscle disorders suchas degenerative muscle disease, muscular dystrophy, muscle atrophy, ormuscle wasting disorders; a fibrotic condition (e.g., a hepatic,pulmonary, vascular and/or ocular fibrotic condition, such as myocardialfibrosis, and idiopathic pulmonary fibrosis (IPF)); metabolic disease(e.g., type II diabetes insulin resistance, hyperglycemia, and obesity);inflammatory disease or conditions, autoimmune disease, cardiovasculardisease (e.g., congestive heart failure, and hypertension); oculardisease such as age-related macular degeneration; pulmonary disease,musculoskeletal disease, skeletal disease such as osteoporosis;neurologic disease; wound healing; weight loss; and cancer (e.g., acarcinoma, myeloma, a bone-loss inducing cancer, pituitary cancer, andgastrointestinal cancer)), which involves measuring the expression levelof ActRII (e.g., ActRIIA or ActRIIB) protein tissue or body fluid froman individual and comparing the measured expression level with astandard ActRII (e.g., ActRIIA or ActRIIB) expression level in normaltissue or body fluid, whereby an increase in ActRII expression levelcompared to the standard is indicative of a disorder treatable by anActRII-binding protein provided herein, such as a full-lengthanti-ActRIIB antibody and antigen-binding antibody fragment as providedherein.

The ActRII-binding proteins provided herein such as, anti-ActRIIantibodies (e.g., full-length ActRII-antibodies and ActRII-bindingantibody fragment, and variants and derivatives thereof) can be used toassay ActRII (e.g., ActRIIB and ActRIIA) levels in a biological sampleusing classical immunohistological methods known to those of skill inthe art (see, e.g., Jalkanen, et al., J. Cell. Biol. 101:976-985 (1985);Jalkanen et al., J. Cell Biol. 105:3087-3096 (1987)). Otherantibody-based methods useful for detecting ActRII protein (e.g.,ActRIIB and ActRIIA) expression include immunoassays, such as the enzymelinked immunosorbent assay (ELISA), immunoprecipitation, or Westernblotting.

By “assaying the expression level of ActRII protein” is intendedqualitatively or quantitatively measuring or estimating the level ofActRII protein in a first biological sample either directly (e.g., bydetermining or estimating absolute protein level) or relatively (e.g.,by comparing to the disease associated polypeptide level in a secondbiological sample). The ActRII protein expression level in the firstbiological sample can be measured or estimated and compared to astandard ActRII protein level, the standard being taken from a secondbiological sample obtained from an individual not having the disorder orbeing determined by averaging levels from a population of individualsnot having the disorder. As will be appreciated in the art, once the“standard” ActRII protein level is known, it can be used repeatedly as astandard for comparison.

By “biological sample” is intended any biological sample obtained froman individual, cell line, tissue culture, or other source of cellspotentially expressing ActRII. Methods for obtaining tissue biopsies andbody fluids from mammals are known in the art.

Kits Comprising ActRII-Binding Proteins

This disclosure further provides kits that include an ActRII-bindingprotein (e.g., an antibody that specifically binds ActRII such as, afull-length ActRII-antibody and an ActRII-binding antibody fragment, andvariants and derivatives thereof) in suitable packaging, and writtenmaterial and that can be used to perform the methods described herein.The written material can include any of the following information:instructions for use, discussion of clinical studies, listing of sideeffects, scientific literature references, package insert materials,clinical trial results, and/or summaries of these and the like. Thewritten material can indicate or establish the activities and/oradvantages of the composition, and/or describe dosing, administration,side effects, drug interactions, or other information useful to thehealth care provider. Such information can be based on the results ofvarious studies, for example, studies using experimental animalsinvolving in vivo models and/or studies based on human clinical trials.The kit can further contain another therapy (e.g., another agent) and/orwritten material such as that described above that serves to provideinformation regarding the other therapy (e.g., the other agent).

In certain aspects, a kit comprises at least one purified ActRII-bindingprotein in one or more containers. In some aspects, the kits contain allof the components necessary and/or sufficient to perform a detectionassay, including all controls, directions for performing assays, and anynecessary software for analysis and presentation of results.

Immunoassays

ActRII-binding proteins (e.g., antibodies that specifically bind ActRII,and ActRII-binding fragments of antibodies that specifically bindActRII, and variants, or derivatives thereof) can be assayed forimmunospecific binding by any method known in the art. The immunoassaysthat can be used include, but are not limited to, competitive andnon-competitive assay systems using techniques such as Western blots,radioimmunoassays (REA), ELISA (enzyme linked immunosorbent assay),“sandwich” immunoassays, immunoprecipitation assays, precipitinreactions, gel diffusion precipitin reactions, immunodiffusion assays,agglutination assays, complement-fixation assays, immunoradiometricassays, fluorescent immunoassays, or protein A immunoassays. Such assaysare routine and known in the art (see, e.g., Ausubel et al., eds, (1994)Current Protocols in Molecular Biology (John Wiley & Sons, Inc., NY)Vol. 1, which is herein incorporated by reference in its entirety).

ActRII-binding proteins (e.g., antibodies that specifically binds ActRIIand ActRII-binding fragments of antibodies that specifically bindActRII, and variants, or derivatives thereof) provided herein can beemployed histologically, as in immunofluorescence, immunoelectronmicroscopy or non-immunological assays, for in situ detection of ActRII(e.g., ActRIIB and ActRIIA) or conserved variants or peptide fragmentsthereof. In situ detection can be accomplished according to methodsknown in the art. Those of ordinary skill in the art will be able todetermine operative and optimal assay conditions for each determinationby employing routine experimentation. Methods suitable for determinationof binding characteristics of an ActRII-binding protein are describedherein or otherwise known in the art. Equipment and software designedfor such kinetic analyses are commercially available (e.g., BIACORE®,BIAevaluation® software, GE Healthcare; KINEXA® Software, SapidyneInstruments).

Unless otherwise indicated, the practice of the disclosure employsconventional techniques of cell biology, cell culture, molecularbiology, transgenic biology, microbiology, recombinant DNA, andimmunology, which are within the skill of the art.

The following examples are offered by way of illustration and not by wayof limitation.

EXAMPLES

The foregoing description of the specific embodiments will so fullyreveal the general nature of the disclosure that others can, by applyingknowledge within the skill of the art, readily modify and/or adapt forvarious applications such specific embodiments, without undueexperimentation, without departing from the general concept of thepresent disclosure. Therefore, such adaptations and modifications areintended to be within the meaning and range of equivalents of thedisclosed embodiments, based on the teaching and guidance presentedherein. It is to be understood that the phraseology or terminologyherein is for the purpose of description and not of limitation, suchthat the terminology or phraseology of the present specification is tobe interpreted by the skilled artisan in light of the teachings andguidance.

The breadth and scope of the present disclosure should not be limited byany of the above-described exemplary embodiments, but should be definedonly in accordance with the following claims and their equivalents.

All publications, patents, patent applications, and/or other documentscited in this application are incorporated by reference in theirentirety for all purposes to the same extent as if each individualpublication, patent, patent application, and/or other document wereindividually indicated to be incorporated by reference for all purposes.

Example 1. Selection, Characterization and Production of ActRII-BindingAntibodies

A multi-round selection procedure was used to select for human IgGantibodies that bind ActRII with high affinity and compete with activinA for binding human ActRII, which is detailed below.

Materials and Methods

Antigens (ActRIIA, ActRIIB, ActRIIA-Fc, and ActRIIB-Fc) werebiotinylated using the EZ-Link Sulfo-NHS-Biotinylation Kit from Pierce.Goat anti-human F(ab′)₂ kappa-FITC (LC-FITC), Extravidin-PE (EA-PE) andstreptavidin-633 (SA-633) were obtained from Southern Biotech, Sigma andMolecular Probes, respectively. Streptavidin MicroBeads and MACS LCseparation columns were purchased from Miltenyi Biotec.

Naïve Discovery

Eight naïve human synthetic yeast libraries each of ˜10⁹ diversity werepropagated as described previously (see, e.g., WO09/036379; WO10/105256;WO12/009568). For the first two rounds of selection, a magnetic beadsorting technique utilizing the Miltenyi MACs system was performed, asdescribed (see, e.g., Siegel et al., J. Immunol. Meth. 286(1-2):141-153(2004)). Briefly, yeast cells (˜10¹⁰ cells/library) were incubated with3 ml of 10 nM biotinylated monomeric ActRII-Fc antigen (ActRIIB-Fc orActRIIA-Fc) for 15 minute at room temperature in FACS wash buffer(phosphate-buffered saline (PBS)/0.1% bovine serum albumin (BSA)). Afterwashing once with 50 ml ice-cold wash buffer, the cell pellet wasresuspended in 40 mL wash buffer, and Streptavidin MicroBeads (500 μl)were added to the yeast and incubated for 15 minutes at 4° C. Next, theyeast were pelleted, resuspended in 5 mL wash buffer, and loaded onto aMiltenyi LS column. After the 5 mL was loaded, the column was washed 3times with 3 ml FACS wash buffer. The column was then removed from themagnetic field, and the yeast were eluted with 5 mL of growth media andthen grown overnight. The following rounds of sorting were performedusing flow cytometry. Approximately 1×10⁸ yeast were pelleted, washedthree times with wash buffer, and incubated with decreasingconcentrations of biotinylated monomeric or ActRII-Fc fusion antigen(100 to 1 nM) under equilibrium conditions at room temperature. Yeastwere then washed twice and stained with LC-FITC (diluted 1:100) andeither SA-633 (diluted 1:500) or EA-PE (diluted 1:50) secondary reagentsfor 15 minutes at 4° C. After washing twice with ice-cold wash buffer,the cell pellets were resuspended in 0.4 mL wash buffer and transferredto strainer-capped sort tubes. Sorting was performed using a FACS ARIAsorter (BD Biosciences) and sort gates were assigned to select forspecific binders relative to a background control. Subsequent rounds ofselection were employed in order to reduce the number non-specificreagent binders utilizing soluble membrane proteins from CHO cells (See,e.g., WO14/179363 and Xu et al., Protein Eng. Des. Sel. 26(10):663-670(2013)), and to identify binders with improved affinity to ActRII(ActRIIB or ActRIIA) using the ActRII-Fc (ActRIIB-Fc and ActRIIA-Fcantigen, respectively). After the final round of sorting, yeast wereplated and individual colonies were picked for characterization and fornomination of clones for affinity maturation.

Affinity Maturation

Binding optimization of naïve clones was carried out utilizing threematuration strategies: light chain diversification; diversification ofCDRH and/CDRH2; and performing sequential VH and VL mutagenesis.

Light chain diversification: Heavy chain plasmids were extracted naïveoutputs (described above) and transformed into a light chain librarywith a diversity of 1×10⁶. Selections were performed as described abovewith one round of MACS sorting and two rounds of FACS sorting using 10nM or 1 nM biotinylated ActRII-Fc antigen (ActRIIB-Fc or ActRIIA-Fc) forrespective rounds.

CDRH1 and CDRH2 selection: The CDRH3s from clones selected from thelight chain diversification procedure of was recombined into a premadelibrary with CDRH1 and CDRH2 variants of a diversity of 1×10⁸ andparallel selections were performed using ActRIIB and ActRIIA antigen,respectively. As described above. Affinity pressures were applied byincubating the biotinylated antigen-antibody yeast complex withunbiotinylated antigen for different amounts of time to select for thehighest affinity antibodies.

VHmut/VKmut selection: Clones obtained from the CDRH1 and CDRH2selection procedure were subject to additional rounds of affinitymaturation via error prone PCR-based mutagenesis of the heavy chainand/or light chain. Selections were performed using ActRIIB or ActRIIAas antigen generally as described above but with the addition ofemploying FACS sorting for all selection rounds. Antigen concentrationwas reduced and cold antigen competition times were increased topressure further for optimal affinity.

Antibody Production and Purification

In order to produce sufficient amounts of selected antibodies forfurther characterization, the yeast clones were grown to saturation andthen induced for 48 h at 30° C. with shaking. After induction, yeastcells were pelleted and the supernatants were harvested forpurification. IgGs were purified using a Protein A column and elutedwith acetic acid, pH 2.0. Fab fragments were generated by papaindigestion and purified over KappaSelect (GE Healthcare LifeSciences).

ForteBio K_(D) Measurements

ForteBio affinity measurements of selected antibodies were performedgenerally as previously described (see, e.g., Estep et al., Mabs,5(2):270-278 (2013)). Briefly, ForteBio affinity measurements wereperformed by loading IgGs on-line onto AHQ sensors. Sensors wereequilibrated off-line in assay buffer for 30 minutes and then monitoredon-line for 60 seconds for baseline establishment. Sensors with loadedIgGs were exposed to 100 nM antigen for 5 minutes, afterwards they weretransferred to assay buffer for 5 minutes for off-rate measurement.Kinetics were analyzed using the 1:1 binding model.

MSD-SET K_(D) Measurements

Equilibrium affinity measurements of selected antibodies were performedgenerally as previously described (Estep et al., Mabs 5(2):270-278(2013)). Briefly, solution equilibrium titrations (SET) were performedin PBS+0.1% IgG-Free BSA (PBSF) with antigen (ActRIIB monomer or ActRIIAmonomer) held constant at 10-100 pM and incubated with 3- to 5-foldserial dilutions of Fab or mAbs starting at 10 pM-10 nM. Antibodies (20nM in PBS) were coated onto standard bind MSD-ECL plates overnight at 4°C. or at room temperature for 30 minutes. Plates were then blocked byBSA for 30 minutes with shaking at 700 rpm, followed by three washeswith wash buffer (PBSF+0.05% Tween 20). SET samples were applied andincubated on the plates for 150 s with shaking at 700 rpm followed byone wash. Antigen captured on a plate was detected with 250 ng/mLsulfotag-labeled streptavidin in PBSF by incubation on the plate for 3minutes. The plates were washed three times with wash buffer and thenread on the MSD Sector Imager 2400 instrument using 1× Read Buffer Twith surfactant. The percent free antigen was plotted as a function oftitrated antibody in Prism and fit to a quadratic equation to extractthe K_(D). To improve throughput, liquid handling robots were usedthroughout MSD-SET experiments, including SET sample preparation.

Octet Red384 Epitope Binning/Ligand Blocking

Epitope binning/ligand blocking of selected antibodies was performedusing a standard sandwich format cross-blocking assay. Controlanti-target IgG was loaded onto AHQ sensors and unoccupied Fc-bindingsites on the sensor were blocked with an irrelevant human IgG1 antibody.The sensors were then exposed to 100 nM target antigen followed by asecond anti-target antibody or ligand. Data was processed usingForteBio's Data Analysis Software 7.0. Additional binding by the secondantibody or ligand after antigen association indicates an unoccupiedepitope (non-competitor), while no binding indicates epitope blocking(competitor or ligand blocking).

Size Exclusion Chromatography

A TSKgel SuperSW mAb HTP column (22855) was used for fast SEC analysisof yeast-produced mAbs at 0.4 mL/minute with a cycle time of 6 min/run.200 mM Sodium Phosphate and 250 mM Sodium Chloride was used as themobile phase.

Dynamic Scanning Fluorimetry

10 uL of 20× Sypro Orange was added to 20 uL of 0.2-1 mg/mL mAb or Fabsolution. An RT-PCR instrument (BioRad CFX96 RT PCR) was used to rampthe sample plate temperature from 40° to 95° C. at 0.5° C. increment,with a 2 minute equilibration at each temperature. The negative of thefirst derivative for the raw data was used to extract Tm.

Based on the foregoing analyses, the sequences of 8 naïve ActRII-bindingantibodies with preferred characteristics were confirmed and chosen forbinding optimization using the maturation strategies described above.

Example 2. Characterization of ActRII-Binding Naïve and OptimizedAntibodies

Exemplary naïve and binding optimized ActRII-binding proteins generatedaccording to the previous example were further characterized bysequence, SPR, and cell-based reporter assay analyses.

Sequences of exemplary naïve and binding optimized ActRII-bindingantibodies generated according to the methods described in Example 1 arepresented in Table 1 (exemplary CDR sequences are underscored).

TABLE 1 Exemplary ActRII-binding proteins ActRIIB-binding Antibodies A01VH CAGCTGCAGCTGCAGGAGTCGGGCCCAGGACTGGTGAAGCCTTCGGAGACCCTGTCCCTCACCTGCACTGTCTCTGGTGGCTCCATCAGCAGTAGTAGTTACGCATGGGGCTGGATCCGCCAGCCCCCAGGGAAGGGGCTGGAGTGGATTGGGAGTATCTATTATAGTGGGAGCACCTACTACAACCCGTCCCTCAAGAGTCGAGTCACCATATCCGTAGACACGTCCAAGAACCAGTTCTCCCTGAAGCTGAGTTCTGTGACCGCCGCAGACACGGCGGTGTACTACTGCGCCAGAGACTCAGGAATAGGATACAGCTACGCCTCATCACATGGCTACTACTACTACATGGACGTATGGGGCAAGGGTACAACTGTCACCGTCTCCTCA(SEQ ID NO: 1) VHQLQLQESGPGLVKPSETLSLTCTVSGGSISSSSYAWGWIRQPPGKGLEWIGSIYYSGSTYYNPSLKSRVTISVDTSKNQFSLKLSSVTAADTAVYYCARDSGIGYSYASSHGYYYYMDVWGKGTTVTVSS(SEQ ID NO: 2)CDR1: GGSISSSSY (SEQ ID NO: 3; nucleotides 26-34 of SEQ ID NO: 2)CDR2: YYSGS (SEQ ID NO: 4; amino acid residues 54-58 of SEQ ID NO: 2)CDR3: DSGIGYSYASSHGYYYYMDV (SEQ ID NO: 5; amino acid residues 100-119of SEQ ID NO: 2) HCAGCTGCAGCTGCAGGAGTCGGGCCCAGGACTGGTGAAGCCTTCGGAGACCCTGTCCCTCACCTGCACTGTCTCTGGTGGCTCCATCAGCAGTAGTAGTTACGCATGGGGCTGGATCCGCCAGCCCCCAGGGAAGGGGCTGGAGTGGATTGGGAGTATCTATTATAGTGGGAGCACCTACTACAACCCGTCCCTCAAGAGTCGAGTCACCATATCCGTAGACACGTCCAAGAACCAGTTCTCCCTGAAGCTGAGTTCTGTGACCGCCGCAGACACGGCGGTGTACTACTGCGCCAGAGACTCAGGAATAGGATACAGCTACGCCTCATCACATGGCTACTACTACTACATGGACGTATGGGGCAAGGGTACAACTGTCACCGTCTCCTCAGCTAGCACAAAAGGACCAAGCGTGTTTCCACTGGCACCTAGCAGCAAATCCACCAGCGGCGGAACAGCAGCCCTCGGGTGCCTGGTGAAGGATTACTTCCCTGAGCCAGTCACAGTGTCCTGGAACTCCGGAGCCCTGACATCCGGCGTGCACACCTTCCCCGCTGTGCTGCAATCCAGCGGACTGTATAGCCTCAGCTCCGTCGTGACAGTCCCTTCCAGCAGCCTGGGCACACAGACTTACATTTGCAACGTGAACCACAAACCTTCCAACACTAAGGTGGACAAAAAGGTGGAACCCAAATCCTGTGATAAGACCCATACATGCCCACCTTGTCCCGCTCCTGAGCTGCTGGGGGGACCTTCCGTCTTTCTGTTTCCTCCAAAACCAAAAGACACACTCATGATCAGCCGGACCCCCGAAGTCACCTGTGTGGTGGTGGACGTCAGCCACGAAGATCCAGAGGTCAAGTTCAATTGGTACGTGGATGGAGTGGAAGTCCACAACGCAAAAACCAAACCTAGAGAAGAACAGTACAATAGCACATACAGGGTGGTGTCCGTCCTGACAGTGCTCCACCAGGACTGGCTCAATGGCAAAGAGTATAAGTGCAAGGTGAGCAACAAGGCCCTGCCTGCACCAATTGAGAAAACAATTAGCAAGGCAAAGGGGCAGCCACGGGAACCCCAGGTGTATACCCTGCCCCCAAGCCGGGATGAACTGACCAAAAACCAGGTCAGCCTGACATGCCTGGTGAAAGGGTTTTACCCAAGCGATATTGCCGTCGAGTGGGAGAGCAACGGACAGCCAGAAAACAATTACAAAACCACCCCACCTGTGCTGGACTCCGATGGGAGCTTTTTCCTGTACAGCAAGCTCACAGTGGACAAGTCCAGATGGCAACAGGGCAACGTGTTTTCCTGCTCCGTGATGCACGAGGCCCTCCACAACCACTATACACAAAAGTCCCTCTCCCTCAGCCCAGGAAAG (SEQ ID NO: 6) HQLQLQESGPGLVKPSETLSLTCTVSGGSISSSSYAWGWIRQPPGKGLEWIGSIYYSGSTYYNPSLKSRVTISVDTSKNQFSLKLSSVTAADTAVYYCARDSGIGYSYASSHGYYYYMDVWGKGTTVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSVFLEPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO: 7) VLGAAATAGTGTTGACGCAGTCTCCAGCCACCCTGTCTGTGTCTCCAGGGGAAAGAGCCACCCTCTCCTGCAGGGCCAGTCAGAGTGTTGGCAGCAACTTAGCCTGGTACCAGCAGAAACCTGGCCAGGCTCCCAGGCTCCTCATCTATGGTGCATCCACCAGGGCCACTGGTATCCCAGCCAGGTTCAGTGGCAGTGGGTCTGGGACAGAGTTCACTCTCACCATCAGCAGCCTGCAGTCTGAAGATTTTGCAGTTTATTACTGTCAGCAGTACTTCCACTTCCCTCTCACTTTTGGCGGAGGGACCAAGGTTGAGATCAAA(SEQ ID NO: 8) VLEIVLTQSPATLSVSPGERATLSCRASQSVGSNLAWYQQKPGQAPRLLIYGASTRATGIPARFSGSGSGILFTLTISSLQSEDFAVYYCQQYFHFPLTEGGGTKVEIK (SEQ ID NO: 9)CDR1: RASQSVGSNLA (SEQ ID NO: 10; amino acid residues 24-34 of SEQ ID NO: 9)CDR2: GASTRAT (SEQ ID NO: 11; amino acid residues 50-56 of SEQ ID NO: 9)CDR3: QQYFHFPLT (SEQ ID NO: 12; amino acid residues 89-97 of SEQ ID NO: 9)L GAAATAGTGTTGACGCAGTCTCCAGCCACCCTGTCTGTGTCTCCAGGGGAAAGAGCCACCCTCTCCTGCAGGGCCAGTCAGAGTGTTGGCAGCAACTTAGCCTGGTACCAGCAGAAACCTGGCCAGGCTCCCAGGCTCCTCATCTATGGTGCATCCACCAGGGCCACTGGTATCCCAGCCAGGTTCAGTGGCAGTGGGTCTGGGACAGAGTTCACTCTCACCATCAGCAGCCTGCAGTCTGAAGATTTTGCAGTTTATTACTGTCAGCAGTACTTCCACTTCCCTCTCACTTTTGGCGGAGGGACCAAGGTTGAGATCAAACGTACGGTGGCTGCACCTTCCGTCTTTATCTTTCCACCTTCCGATGAGCAGCTGAAGAGCGGAACAGCAAGCGTGGTGTGTCTGCTGAACAACTTTTATCCCCGGGAGGCAAAGGTGCAGTGGAAAGTCGACAATGCTCTCCAGTCCGGCAATTCCCAAGAGAGCGTGACAGAGCAAGATTCCAAGGACTCCACTTACAGCCTGTCCAGCACCCTCACACTGAGCAAGGCTGATTACGAGAAACACAAAGTGTACGCTTGTGAAGTCACCCACCAAGGCCTGAGCAGCCCAGTCACTAAGTCCTTTAACCGGGGCGAATGT (SEQ ID NO: 13) LEIVLTQSPATLSVSPGERATLSCRASQSVGSNLAWYQQKPGQAPRLLIYGASTRATGIPARFSGSGSGILFTLTISSLQSEDFAVYYCQQYFHFPLTEGGGTKVEIKRTVAAPSVFIFPPSDEQLKSGTASVVCLLNNFYPREAKVQWKVDNALQSGNSQESVFLQDSKDSTYSLSSTLTLSKADYEKHKVYACEVTHQGLSSPVTKSFNRGEC (SEQ ID NO: 14) E01 VHCAGGTGCAGCTGCAGGAGTCGGGCCCAGGACTGGTGAAGCCTTCACAGACCCTGTCCCTCACCTGTACTGTCTCTGGTGGCTCCATCGGGAGTGGTGGTTACTACTGGAGCTGGATCCGCCAGCACCCAGGGAAGGGCCTGGAGTGGATTGGGGGGATCTATGGTAGTGGGAGCACCTACTACAACCCGTCCCTCAAGAGTCGAGTTACCATATCAGTAGACACGTCTAAGAACCAGTTCTCCCTGAAGCTGAGTTCTGTGACCGCCGCAGACACGGCGGTGTACTACTGCGCCAGAGACTCAGGAATAGGATACAGCTACGCCTCATCACATGGCTACTACTACTACATGGACGTATGGGGCAAGGGTACAACTGTCACCGTCTCCTCA (SEQ ID NO: 15) VHQVQLQESGPGLVKPSQTLSLTCTVSGGSIGSGGYYWSWIRQHPGKGLEWIGGIYGSGSTYYNPSLKSRVTISVDTSKNQFSLKLSSVTAADTAVYYCARDSGIGYSYASSHGYYYYMDVWGKGTTVTVSS(SEQ ID NO: 16)CDR1: GGSIGSGGY (SEQ ID NO: 17; amino acid residues 26-34 of SEQ ID NO: 16)CDR2: YGSG (SEQ ID NO: 18; amino acid residues 54-57 of SEQ ID NO: 16)CDR3: DSGIGYSYASSHGYYYYMDV (SEQ ID NO: 5; amino acid residues 100-119of SEQ ID NO: 16) HCAGGTGCAGCTGCAGGAGTCGGGCCCAGGACTGGTGAAGCCTTCACAGACCCTGTCCCTCACCTGTACTGTCTCTGGTGGCTCCATCGGGAGTGGTGGTTACTACTGGAGCTGGATCCGCCAGCACCCAGGGAAGGGCCTGGAGTGGATTGGGGGGATCTATGGTAGTGGGAGCACCTACTACAACCCGTCCCTCAAGAGTCGAGTTACCATATCAGTAGACACGTCTAAGAACCAGTTCTCCCTGAAGCTGAGTTCTGTGACCGCCGCAGACACGGCGGTGTACTACTGCGCCAGAGACTCAGGAATAGGATACAGCTACGCCTCATCACATGGCTACTACTACTACATGGACGTATGGGGCAAGGGTACAACTGTCACCGTCTCCTCAGCTAGCACAAAAGGACCAAGCGTGTTTCCACTGGCACCTAGCAGCAAATCCACCAGCGGCGGAACAGCAGCCCTCGGGTGCCTGGTGAAGGATTACTTCCCTGAGCCAGTCACAGTGTCCTGGAACTCCGGAGCCCTGACATCCGGCGTGCACACCTTCCCCGCTGTGCTGCAATCCAGCGGACTGTATAGCCTCAGCTCCGTCGTGACAGTCCCTTCCAGCAGCCTGGGCACACAGACTTACATTTGCAACGTGAACCACAAACCTTCCAACACTAAGGTGGACAAAAAGGTGGAACCCAAATCCTGTGATAAGACCCATACATGCCCACCTTGTCCCGCTCCTGAGCTGCTGGGGGGACCTTCCGTCTTTCTGTTTCCTCCAAAACCAAAAGACACACTCATGATCAGCCGGACCCCCGAAGTCACCTGTGTGGTGGTGGACGTCAGCCACGAAGATCCAGAGGTCAAGTTCAATTGGTACGTGGATGGAGTGGAAGTCCACAACGCAAAAACCAAACCTAGAGAAGAACAGTACAATAGCACATACAGGGTGGTGTCCGTCCTGACAGTGCTCCACCAGGACTGGCTCAATGGCAAAGAGTATAAGTGCAAGGTGAGCAACAAGGCCCTGCCTGCACCAATTGAGAAAACAATTAGCAAGGCAAAGGGGCAGCCACGGGAACCCCAGGTGTATACCCTGCCCCCAAGCCGGGATGAACTGACCAAAAACCAGGTCAGCCTGACATGCCTGGTGAAAGGGTTTTACCCAAGCGATATTGCCGTCGAGTGGGAGAGCAACGGACAGCCAGAAAACAATTACAAAACCACCCCACCTGTGCTGGACTCCGATGGGAGCTTTTTCCTGTACAGCAAGCTCACAGTGGACAAGTCCAGATGGCAACAGGGCAACGTGTTTTCCTGCTCCGTGATGCACGAGGCCCTCCACAACCACTATACACAAAAGTCCCTCTCCCTCAGCCCAGGAAAG (SEQ ID NO: 19) HQVQLQESGPGLVKPSQTLSLTCTVSGGSIGSGGYYWSWIRQHPGKGLEWIGGIYGSGSTYYNPSLKSRVTISVDTSKNQFSLKLSSVTAADTAVYYCARDSGIGYSYASSHGYYYYMDVWGKGTTVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSVFLEPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFELYSKLTVDKSRWQQGNVESCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO: 20) VLSEQ ID NO: 8 VLEIVLTQSPATLSVSPGERATLSCRASQSVGSNLAWYQQKPGQAPRLLIYGASTRATGIPARFSGSGSGILFTLTISSLQSEDFAVYYCQQYFHFPLTFGGGTKVEIK (SEQ ID NO: 9)CDR1: RASQSVGSNLA (SEQ ID NO: 10; amino acid residues 24-34 of SEQ ID NO: 9)CDR2: GASTRAT (SEQ ID NO: 11; amino acid residues 50-56 of SEQ ID NO: 9)CDR3: QQYFHFPLT (SEQ ID NO: 12; amino acid residues 89-97 of SEQ ID NO: 9)L SEQ ID NO: 13 L SEQ ID NO: 14 F01 VHCAGGTGCAGCTGCAGGAGTCGGGCCCAGGACTGGTGAAGCCTTCACAGACCCTGTCCCTCACCTGTACTGTCTCTGGTGGCTCCATCAAGAGTGGTGGGTACTACTGGAGCTGGATCCGCCAGCACCCAGGGAAGGGCCTGGAGTGGATTGGGGGGATCTATCCGAGTGGGAGCACCTACTACAACCCGTCCCTCAAGAGTCGAGTTACCATATCAGTAGACACGTCTAAGAACCAGTTCTCCCTGAAGCTGAGTTCTGTGACCGCCGCAGACACGGCGGTGTACTACTGCGCCAGAGACTCAGGAATAGGATACAGCTACGCCTCATCACATGGCTACTACTACTACATGGACGTATGGGGCAAGGGTACAACTGTCACCGTCTCCTCA(SEQ ID NO: 21) VHQVQLQESGPGLVKPSQTLSLTCTVSGGSIKSGGYYWSWIRQHPGKGLEWIGGIYPSGSTYYNPSLKSRVTISVDTSKNQFSLKLSSVTAADTAVYYCARDSGIGYSYASSHGYYYYMDVWGKGTTVTVSS (SEQ ID NO: 22)CDR1: GGSIKSGGY (SEQ ID NO: 23; amino acid residues 26-34 of SEQ ID NO: 22)CDR2: WIGGIYPSGSTYY (SEQ ID NO: 24; amino acid residues 49-61 of SEQ ID NO: 22)CDR3: DSGIGYSYASSHGYYYYMDV (SEQ ID NO: 5; amino acid residues 100-119of SEQ ID NO: 22) HCAGGTGCAGCTGCAGGAGTCGGGCCCAGGACTGGTGAAGCCTTCACAGACCCTGTCCCTCACCTGTACTGTCTCTGGTGGCTCCATCAAGAGTGGTGGGTACTACTGGAGCTGGATCCGCCAGCACCCAGGGAAGGGCCTGGAGTGGATTGGGGGGATCTATCCGAGTGGGAGCACCTACTACAACCCGTCCCTCAAGAGTCGAGTTACCATATCAGTAGACACGTCTAAGAACCAGTTCTCCCTGAAGCTGAGTTCTGTGACCGCCGCAGACACGGCGGTGTACTACTGCGCCAGAGACTCAGGAATAGGATACAGCTACGCCTCATCACATGGCTACTACTACTACATGGACGTATGGGGCAAGGGTACAACTGTCACCGTCTCCTCAGCTAGCACAAAAGGACCAAGCGTGTTTCCACTGGCACCTAGCAGCAAATCCACCAGCGGCGGAACAGCAGCCCTCGGGTGCCTGGTGAAGGATTACTTCCCTGAGCCAGTCACAGTGTCCTGGAACTCCGGAGCCCTGACATCCGGCGTGCACACCTTCCCCGCTGTGCTGCAATCCAGCGGACTGTATAGCCTCAGCTCCGTCGTGACAGTCCCTTCCAGCAGCCTGGGCACACAGACTTACATTTGCAACGTGAACCACAAACCTTCCAACACTAAGGTGGACAAAAAGGTGGAACCCAAATCCTGTGATAAGACCCATACATGCCCACCTTGTCCCGCTCCTGAGCTGCTGGGGGGACCTTCCGTCTTTCTGTTTCCTCCAAAACCAAAAGACACACTCATGATCAGCCGGACCCCCGAAGTCACCTGTGTGGTGGTGGACGTCAGCCACGAAGATCCAGAGGTCAAGTTCAATTGGTACGTGGATGGAGTGGAAGTCCACAACGCAAAAACCAAACCTAGAGAAGAACAGTACAATAGCACATACAGGGTGGTGTCCGTCCTGACAGTGCTCCACCAGGACTGGCTCAATGGCAAAGAGTATAAGTGCAAGGTGAGCAACAAGGCCCTGCCTGCACCAATTGAGAAAACAATTAGCAAGGCAAAGGGGCAGCCACGGGAACCCCAGGTGTATACCCTGCCCCCAAGCCGGGATGAACTGACCAAAAACCAGGTCAGCCTGACATGCCTGGTGAAAGGGTTTTACCCAAGCGATATTGCCGTCGAGTGGGAGAGCAACGGACAGCCAGAAAACAATTACAAAACCACCCCACCTGTGCTGGACTCCGATGGGAGCTTTTTCCTGTACAGCAAGCTCACAGTGGACAAGTCCAGATGGCAACAGGGCAACGTGTTTTCCTGCTCCGTGATGCACGAGGCCCTCCACAACCACTATACACAAAAGTCCCTCTCCCTCAGCCCAGGAAAG (SEQ ID NO: 25) HQVQLQESGPGLVKPSQTLSLTCTVSGGSIKSGGYYWSWIRQHPGKGLEWIGGIYPSGSTYYNPSLKSRVTISVDTSKNQFSLKLSSVTAADTAVYYCARDSGIGYSYASSHGYVYYMDVWGKGTTVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSVFLEPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFELYSKLTVDKSRWQQGNVESCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO: 26) VLSEQ ID NO: 8 VLEIVLTQSPATLSVSPGERATLSCRASQSVGSNLAWYQQKPGQAPRLLIVGASTRATGIPARFSGSGSGTEFTLTISSLQSEDFAVYYCQQYFHFPLTFGGGTKVEIK (SEQ ID NO: 9)CDR1: RASQSVGSNLA (SEQ ID NO: 10; amino acid residues 24-34 of SEQ ID NO: 9)CDR2: GASTRAT (SEQ ID NO: 11; amino acid residues 50-56 of SEQ ID NO: 9)CDR3: QQYFHFPLT (SEQ ID NO: 12; amino acid residues 89-97 of SEQ ID NO: 9)L SEQ ID NO: 13 L SEQ ID NO: 14 B01 VHCAGGTGCAGCTGCAGGAGTCGGGCCCAGGACTGGTGAAGCCTTCACAGACCCTGTCCCTCACCTGTACTGTCTCTGGTGGCTCCATCGAGAGCGGTGGTTACTACTGGAGCTGGATCCGCCAGCACCCAGGGAAGGGCCTGGAGTGGATTGGGGGTATCTATGGGAGTGGGAGCACCTACTACAACCCGTCCCTCAAGAGTCGAGTTACCATATCAGTAGACACGTCTAAGAACCAGTTCTCCCTGAAGCTGAGTTCTGTGACCGCCGCAGACACGGCGGTGTACTACTGCGCCAGAGACTCAGGAATAGGATACAGCTACGCCTCATCACATGGCTACTACTACTACATGGACGTATGGGGCAAGGGTACAACTGTCACCGTCTCCTCA (SEQ ID NO: 27) VHQVQLQESGPGLVKPSQTLSLTCTVSGGSILSGGYYWSWIRQHPGKGLEWIGGIYYSGKTYYNPSLKSRVTISVDTSKNQFSLKLSSVTAADTAVYYCARDSGIGYSYASSHGYVYYMDVWGKGTTVTVSS(SEQ ID NO: 28)CDR1: GGSILSGGY (SEQ ID NO: 29; amino acid residues 26-34 of SEQ ID NO: 28)CDR2: YYSGK (SEQ ID NO: 30; amino acid residues 54-58 of SEQ ID NO: 28)CDR3: DSGIGYSYASSHGYYYYMDV (SEQ ID NO: 5; amino acid residues 100-119 of SEQ ID NO: 28) HCAGGTGCAGCTGCAGGAGTCGGGCCCAGGACTGGTGAAGCCTTCACAGACCCTGTCCCTCACCTGTACTGTCTCTGGTGGCTCCATCGAGAGCGGTGGTTACTACTGGAGCTGGATCCGCCAGCACCCAGGGAAGGGCCTGGAGTGGATTGGGGGTATCTATGGGAGTGGGAGCACCTACTACAACCCGTCCCTCAAGAGTCGAGTTACCATATCAGTAGACACGTCTAAGAACCAGTTCTCCCTGAAGCTGAGTTCTGTGACCGCCGCAGACACGGCGGTGTACTACTGCGCCAGAGACTCAGGAATAGGATACAGCTACGCCTCATCACATGGCTACTACTACTACATGGACGTATGGGGCAAGGGTACAACTGTCACCGTCTCCTCAGCTAGCACAAAAGGACCAAGCGTGTTTCCACTGGCACCTAGCAGCAAATCCACCAGCGGCGGAACAGCAGCCCTCGGGTGCCTGGTGAAGGATTACTTCCCTGAGCCAGTCACAGTGTCCTGGAACTCCGGAGCCCTGACATCCGGCGTGCACACCTTCCCCGCTGTGCTGCAATCCAGCGGACTGTATAGCCTCAGCTCCGTCGTGACAGTCCCTTCCAGCAGCCTGGGCACACAGACTTACATTTGCAACGTGAACCACAAACCTTCCAACACTAAGGTGGACAAAAAGGTGGAACCCAAATCCTGTGATAAGACCCATACATGCCCACCTTGTCCCGCTCCTGAGCTGCTGGGGGGACCTTCCGTCTTTCTGTTTCCTCCAAAACCAAAAGACACACTCATGATCAGCCGGACCCCCGAAGTCACCTGTGTGGTGGTGGACGTCAGCCACGAAGATCCAGAGGTCAAGTTCAATTGGTACGTGGATGGAGTGGAAGTCCACAACGCAAAAACCAAACCTAGAGAAGAACAGTACAATAGCACATACAGGGTGGTGTCCGTCCTGACAGTGCTCCACCAGGACTGGCTCAATGGCAAAGAGTATAAGTGCAAGGTGAGCAACAAGGCCCTGCCTGCACCAATTGAGAAAACAATTAGCAAGGCAAAGGGGCAGCCACGGGAACCCCAGGTGTATACCCTGCCCCCAAGCCGGGATGAACTGACCAAAAACCAGGTCAGCCTGACATGCCTGGTGAAAGGGTTTTACCCAAGCGATATTGCCGTCGAGTGGGAGAGCAACGGACAGCCAGAAAACAATTACAAAACCACCCCACCTGTGCTGGACTCCGATGGGAGCTTTTTCCTGTACAGCAAGCTCACAGTGGACAAGTCCAGATGGCAACAGGGCAACGTGTTTTCCTGCTCCGTGATGCACGAGGCCCTCCACAACCACTATACACAAAAGTCCCTCTCCCTCAGCCCAGGAAAG (SEQ ID NO: 31) HQVQLQESGPGLVKPSQTLSLTCTVSGGSIESGGYYWSWIRQHPGKGLEWIGGIYGSGSTYYNPSLKSRVTISVDTSKNQFSLKLSSVTAADTAVYYCARDSGIGYSYASSHGYYYYMDVWGKGTTVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSVFLEPPKPKDTLMISRTPEVTCVVVDVSHEDPEVFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFELYSKLTVDKSRWQQGNVESCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO: 32) VLSEQ ID NO: 8 VLEIVLTQSPATLSVSPGERATLSCRASQSVGSNLAWYQQKPGQAPRLLIYGASTRATGIPARFSGSGSGTEFTLTISSLQSEDFAVYYCQQYFHFPLTFGGGTKVEIK (SEQ ID NO: 9)CDR1: RASQSVGSNLA (SEQ ID NO: 10; amino acid residues 24-34 of SEQ ID NO: 9)CDR2: GASTRAT (SEQ ID NO: 11; amino acid residues 50-56 of SEQ ID NO: 9)CDR3: QQYFHFPLT (SEQ ID NO: 12; amino acid residues 89-97 of SEQ ID NO: 9)L SEQ ID NO: 13 L SEQ ID NO: 14 C01 VHCAGGTGCAGCTGCAGGAGTCGGGCCCAGGACTGGTGAAGCCTTCACAGACCCTGTCCCTCACCTGTACTGTCTCTGGTGGCTCCATCTCTAGTGGTGGTTACTTTTGGAGCTGGATCCGCCAGCACCCAGGGAAGGGCCTGGAGTGGATTGGGGGGATCTATTACAGTGGGCGGACCTACTACAACCCGTCCCTCAAGAGTCGAGTTACCATATCAGTAGACACGTCTAAGAACCAGTTCTCCCTGAAGCTGAGTTCTGTGACCGCCGCAGACACGGCGGTGTACTACTGCGCCAGAGACTCAGGAATAGGATACAGCTACGCCTCATCACATGGCTACTACTACTACATGGACGTATGGGGCAAGGGTACAACTGTCACCGTCTCCTCA(SEQ ID NO: 33) VHQVQLQESGPGLVKPSQTLSLTCTVSGGSISSGGYFWSWIRQHPGKGLEWIGGIYYSGRTYYNPSLKSRVTISVDTSKNQFSLKLSSVTAADTAVYYCARDSGIGYSYASSHGYYYYMDVWGKGTTVTVSS(SEQ ID NO: 34)CDR1: GGSISSGGY (SEQ ID NO: 35; amino acid residues 26-34 of SEQ ID NO: 34)CDR2: YYSGRT (SEQ ID NO: 36; amino acid residues 54-58 of SEQ ID NO: 34)CDR3: DSGIGYSYASSHGYVYYMDV (SEQ ID NO: 5; amino acid residues 100-119 of SEQ ID NO: 34) HCAGGTGCAGCTGCAGGAGTCGGGCCCAGGACTGGTGAAGCCTTCACAGACCCTGTCCCTCACCTGTACTGTCTCTGGTGGCTCCATCTCTAGTGGTGGTTACTTTTGGAGCTGGATCCGCCAGCACCCAGGGAAGGGCCTGGAGTGGATTGGGGGGATCTATTACAGTGGGCGGACCTACTACAACCCGTCCCTCAAGAGTCGAGTTACCATATCAGTAGACACGTCTAAGAACCAGTTCTCCCTGAAGCTGAGTTCTGTGACCGCCGCAGACACGGCGGTGTACTACTGCGCCAGAGACTCAGGAATAGGATACAGCTACGCCTCATCACATGGCTACTACTACTACATGGACGTATGGGGCAAGGGTACAACTGTCACCGTCTCCTCAGCTAGCACAAAAGGACCAAGCGTGTTTCCACTGGCACCTAGCAGCAAATCCACCAGCGGCGGAACAGCAGCCCTCGGGTGCCTGGTGAAGGATTACTTCCCTGAGCCAGTCACAGTGTCCTGGAACTCCGGAGCCCTGACATCCGGCGTGCACACCTTCCCCGCTGTGCTGCAATCCAGCGGACTGTATAGCCTCAGCTCCGTCGTGACAGTCCCTTCCAGCAGCCTGGGCACACAGACTTACATTTGCAACGTGAACCACAAACCTTCCAACACTAAGGTGGACAAAAAGGTGGAACCCAAATCCTGTGATAAGACCCATACATGCCCACCTTGTCCCGCTCCTGAGCTGCTGGGGGGACCTTCCGTCTTTCTGTTTCCTCCAAAACCAAAAGACACACTCATGATCAGCCGGACCCCCGAAGTCACCTGTGTGGTGGTGGACGTCAGCCACGAAGATCCAGAGGTCAAGTTCAATTGGTACGTGGATGGAGTGGAAGTCCACAACGCAAAAACCAAACCTAGAGAAGAACAGTACAATAGCACATACAGGGTGGTGTCCGTCCTGACAGTGCTCCACCAGGACTGGCTCAATGGCAAAGAGTATAAGTGCAAGGTGAGCAACAAGGCCCTGCCTGCACCAATTGAGAAAACAATTAGCAAGGCAAAGGGGCAGCCACGGGAACCCCAGGTGTATACCCTGCCCCCAAGCCGGGATGAACTGACCAAAAACCAGGTCAGCCTGACATGCCTGGTGAAAGGGTTTTACCCAAGCGATATTGCCGTCGAGTGGGAGAGCAACGGACAGCCAGAAAACAATTACAAAACCACCCCACCTGTGCTGGACTCCGATGGGAGCTTTTTCCTGTACAGCAAGCTCACAGTGGACAAGTCCAGATGGCAACAGGGCAACGTGTTTTCCTGCTCCGTGATGCACGAGGCCCTCCACAACCACTATACACAAAAGTCCCTCTCCCTCAGCCCAGGAAAG (SEQ ID NO: 37) HQVQLQESGPGLVKPSQTLSLTCTVSGGSISSGGYFWSWIRQHPGKGLEWIGGIYYSGRTYYNPSLKSRVTISVDTSKNQFSLKLSSVTAADTAVYYCARDSGIGYSYASSHGYYYYMDVWGKGTTVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSVFLEPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFELYSKLTVDKSRWQQGNVESCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO: 38) VLSEQ ID NO: 8 VLEIVLTQSPATLSVSPGERATLSCRASQSVGSNLAWYQQKPGQAPRLLIYGASTRATGIPARFSGSGSGILFTLTISSLQSEDFAVYYCQQYFHFPLTFGGGTKVEIK (SEQ ID NO: 9)CDR1: RASQSVGSNLA (SEQ ID NO: 10; amino acid residues 24-34 of SEQ ID NO: 9)CDR2: GASTRAT (SEQ ID NO: 11; amino acid residues 50-56 of SEQ ID NO: 9)CDR3: QQYFHFPLT (SEQ ID NO: 12; amino acid residues 89-97 of SEQ ID NO: 9)L SEQ ID NO: 13 L SEQ ID NO: 14 D01 VHCAGGTGCAGCTGCAGGAGTCGGGCCCAGGACTGGTGAAGCCTTCACAGACCCTGTCCCTCACCTGTACTGTCTCTGGTGGCTCCATCGAGAGCGGTGGTTACTACTGGAGCTGGATCCGCCAGCACCCAGGGAAGGGCCTGGAGTGGATTGGGGGTATCTATGGGAGTGGGAGCACCTACTACAACCCGTCCCTCAAGAGTCGAGTTACCATATCAGTAGACACGTCTAAGAACCAGTTCTCCCTGAAGCTGAGTTCTGTGACCGCCGCAGACACGGCGGTGTACTACTGCGCCAGAGACTCAGGAATAGGATACAGCTACGCCTCATCACATGGCTACTACTACTACATGGACGTATGGGGCAAGGGTACAACTGTCACCGTCTCCTCA)(SEQ ID NO: 39) VHQVQLQESGPGLVKPSQTLSLTCTVSGGSIESGGYYWSWIRQHPGKGLEWIGGIYGSGSTYYNPSLKSRVTISVDTSKNQFSLKLSSVTAADTAVYYCARDSGIGYSYASSHGYYYYMDVWGKGTTVTVSS(SEQ ID NO: 40)CDR1: GGSIESGGY (SEQ ID NO: 41; amino acid residues 26-34 of SEQ ID NO: 40)CDR2: YGSGS (SEQ ID NO: 178; amino acid residues 54-58 of SEQ ID NO: 40)CDR3: DSGIGYSYASSHGYYYYMDV (SEQ ID NO: 5; amino acid residues 100-119 of SEQ ID NO: 40) HCAGGTGCAGCTGCAGGAGTCGGGCCCAGGACTGGTGAAGCCTTCACAGACCCTGTCCCTCACCTGTACTGTCTCTGGTGGCTCCATCGAGAGCGGTGGTTACTACTGGAGCTGGATCCGCCAGCACCCAGGGAAGGGCCTGGAGTGGATTGGGGGTATCTATGGGAGTGGGAGCACCTACTACAACCCGTCCCTCAAGAGTCGAGTTACCATATCAGTAGACACGTCTAAGAACCAGTTCTCCCTGAAGCTGAGTTCTGTGACCGCCGCAGACACGGCGGTGTACTACTGCGCCAGAGACTCAGGAATAGGATACAGCTACGCCTCATCACATGGCTACTACTACTACATGGACGTATGGGGCAAGGGTACAACTGTCACCGTCTCCTCAGCTAGCACAAAAGGACCAAGCGTGTTTCCACTGGCACCTAGCAGCAAATCCACCAGCGGCGGAACAGCAGCCCTCGGGTGCCTGGTGAAGGATTACTTCCCTGAGCCAGTCACAGTGTCCTGGAACTCCGGAGCCCTGACATCCGGCGTGCACACCTTCCCCGCTGTGCTGCAATCCAGCGGACTGTATAGCCTCAGCTCCGTCGTGACAGTCCCTTCCAGCAGCCTGGGCACACAGACTTACATTTGCAACGTGAACCACAAACCTTCCAACACTAAGGTGGACAAAAAGGTGGAACCCAAATCCTGTGATAAGACCCATACATGCCCACCTTGTCCCGCTCCTGAGCTGCTGGGGGGACCTTCCGTCTTTCTGTTTCCTCCAAAACCAAAAGACACACTCATGATCAGCCGGACCCCCGAAGTCACCTGTGTGGTGGTGGACGTCAGCCACGAAGATCCAGAGGTCAAGTTCAATTGGTACGTGGATGGAGTGGAAGTCCACAACGCAAAAACCAAACCTAGAGAAGAACAGTACAATAGCACATACAGGGTGGTGTCCGTCCTGACAGTGCTCCACCAGGACTGGCTCAATGGCAAAGAGTATAAGTGCAAGGTGAGCAACAAGGCCCTGCCTGCACCAATTGAGAAAACAATTAGCAAGGCAAAGGGGCAGCCACGGGAACCCCAGGTGTATACCCTGCCCCCAAGCCGGGATGAACTGACCAAAAACCAGGTCAGCCTGACATGCCTGGTGAAAGGGTTTTACCCAAGCGATATTGCCGTCGAGTGGGAGAGCAACGGACAGCCAGAAAACAATTACAAAACCACCCCACCTGTGCTGGACTCCGATGGGAGCTTTTTCCTGTACAGCAAGCTCACAGTGGACAAGTCCAGATGGCAACAGGGCAACGTGTTTTCCTGCTCCGTGATGCACGAGGCCCTCCACAACCACTATACACAAAAGTCCCTCTCCCTCAGCCCAGGAAAG (SEQ ID NO: 42) HQVQLQESGPGLVKPSQTLSLTCTVSGGSIESGGYYWSWIRQHPGKGLEWIGGIYGSGSTYYNPSLKSRVTISVDTSKNQFSLKLSSVTAADTAVYYCARDSGIGYSYASSHGYYYYMDVWGKGTTVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSVFLEPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFELYSKLTVDKSRWQQGNVESCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO: 43) VLSEQ ID NO: 8 VLEIVLTQSPATLSVSPGERATLSCRASQSVGSNLAWYQQKPGQAPRLLIYGASTRATGIPARFSGSGSGTEFTLTISSLQSEDFAVYYCQQYFHFPLTFGGGTKVEIK (SEQ ID NO: 9)CDR1: RASQSVGSNLA (SEQ ID NO: 10; amino acid residues 24-34 of SEQ ID NO: 9)CDR2: GASTRAT (SEQ ID NO: 11; amino acid residues 50-56 of SEQ ID NO: 9)CDR3: QQYFHFPLT (SEQ ID NO: 12; amino acid residues 89-97 of SEQ ID NO: 9)L SEQ ID NO: 13 L SEQ ID NO: 14 G01 VHCAGCTGCAGCTGCAGGAGTCGGGCCCAGGACTGGTGAAGCCTTCGGAGACCCTGTCCCTCACCTGCACTGTCTCTGGTGGCTCCATCAGCAGTAGTAGTTACGCATGGGGCTGGATCCGCCAGCCCCCAGGGAAGGGGCTGGAGTGGATTGGGAGTATCTATTATAGTGGGAGCACCTACTACAACCCGTCCCTCAAGAGTCGAGTCACCATATCCGTAGACACGTCCAAGAACCAGTTCTCCCTGAAGCTGAGTTCTGTGACCGCCGCAGACACGGCGGTGTACTACTGCGCCAGAGCTGGAAAATACCGATGGCACGGAATGGACGTATGGGGCCAGGGAACAACTGTCACCGTCTCCTCA (SEQ ID NO: 44) VHQLQLQESGPGLVKPSETLSLTCTVSGGSISSSSYAWGWIRQPPGKGLEWIGSIYYSGSTYYNPSLKSRVTISVDTSKNQFSLKLSSVTAADTAVYYCARAGKYRWHGMDVWGQGTTVTVSS (SEQ ID NO: 45)CDR1: GGSISSSSY (SEQ ID NO: 3; amino acid residues 26-34 of SEQ ID NO: 45)CDR2: YYSGS (SEQ ID NO: 4; amino acid residues 54-58 of SEQ ID NO: 45)CDR3: AGKYRWHGMDV (SEQ ID NO: 46; amino acid residues 100-110 of SEQ ID NO: 45)H CAGCTGCAGCTGCAGGAGTCGGGCCCAGGACTGGTGAAGCCTTCGGAGACCCTGTCCCTCACCTGCACTGTCTCTGGTGGCTCCATCAGCAGTAGTAGTTACGCATGGGGCTGGATCCGCCAGCCCCCAGGGAAGGGGCTGGAGTGGATTGGGAGTATCTATTATAGTGGGAGCACCTACTACAACCCGTCCCTCAAGAGTCGAGTCACCATATCCGTAGACACGTCCAAGAACCAGTTCTCCCTGAAGCTGAGTTCTGTGACCGCCGCAGACACGGCGGTGTACTACTGCGCCAGAGCTGGAAAATACCGATGGCACGGAATGGACGTATGGGGCCAGGGAACAACTGTCACCGTCTCCTCAGCTAGCACAAAAGGACCAAGCGTGTTTCCACTGGCACCTAGCAGCAAATCCACCAGCGGCGGAACAGCAGCCCTCGGGTGCCTGGTGAAGGATTACTTCCCTGAGCCAGTCACAGTGTCCTGGAACTCCGGAGCCCTGACATCCGGCGTGCACACCTTCCCCGCTGTGCTGCAATCCAGCGGACTGTATAGCCTCAGCTCCGTCGTGACAGTCCCTTCCAGCAGCCTGGGCACACAGACTTACATTTGCAACGTGAACCACAAACCTTCCAACACTAAGGTGGACAAAAAGGTGGAACCCAAATCCTGTGATAAGACCCATACATGCCCACCTTGTCCCGCTCCTGAGCTGCTGGGGGGACCTTCCGTCTTTCTGTTTCCTCCAAAACCAAAAGACACACTCATGATCAGCCGGACCCCCGAAGTCACCTGTGTGGTGGTGGACGTCAGCCACGAAGATCCAGAGGTCAAGTTCAATTGGTACGTGGATGGAGTGGAAGTCCACAACGCAAAAACCAAACCTAGAGAAGAACAGTACAATAGCACATACAGGGTGGTGTCCGTCCTGACAGTGCTCCACCAGGACTGGCTCAATGGCAAAGAGTATAAGTGCAAGGTGAGCAACAAGGCCCTGCCTGCACCAATTGAGAAAACAATTAGCAAGGCAAAGGGGCAGCCACGGGAACCCCAGGTGTATACCCTGCCCCCAAGCCGGGATGAACTGACCAAAAACCAGGTCAGCCTGACATGCCTGGTGAAAGGGTTTTACCCAAGCGATATTGCCGTCGAGTGGGAGAGCAACGGACAGCCAGAAAACAATTACAAAACCACCCCACCTGTGCTGGACTCCGATGGGAGCTTTTTCCTGTACAGCAAGCTCACAGTGGACAAGTCCAGATGGCAACAGGGCAACGTGTTTTCCTGCTCCGTGATGCACGAGGCCCTCCACAACCACTATACACAAAAGTCCCTCTCCCTCAGCCCAGGAAAG (SEQ ID NO: 47) HQLQLQESGPGLVKPSETLSLTCTVSGGSISSSSYAWGWIRQPPGKGLEWIGSIYYSGSTYYNPSLKSRVTISVDTSKNQFSLKLSSVTAADTAVYYCARAGKYRWHGMDVWGQGTTVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO: 48) VLGACATCCAGATGACCCAGTCTCCATCTTCCGTGTCTGCATCTGTAGGAGACAGAGTCACCATCACTTGTCGGGCGAGTCAGGGTATTAGCAGCTGGTTAGCCTGGTATCAGCAGAAACCAGGGAAAGCCCCTAAGCTCCTGATCTATGCTGCATCCAATTTGCAAAGTGGGGTCCCATCAAGGTTCAGCGGCAGTGGATCTGGGACAGATTTCACTCTCACCATCAGCAGCCTGCAGCCTGAAGATTTTGCAACTTATTACTGTCAGCAGGCACCCGACCTCCCTATCACTTTTGGCGGAGGGACCAAGGTTGAGATCAAA (SEQ ID NO: 49)VLDIQMTQSPSSVSASVGDRVTITCRASQGISSWLAWYQQKPGKAPKLLIYAASNLQSGVPSRFSGSGSGTDFTLTISSLQPEDFATYYCQQAPDLPITFGGGTKVEIK (SEQ ID NO: 50)CDR1: RASQGISSWLA (SEQ ID NO: 51; amino acid residues 24-34 of SEQ ID NO: 50)CDR2: AASNLQS (SEQ ID NO: 52; amino acid residues 50-56 of SEQ ID NO: 50)CDR3: QQAPDLPIT (SEQ ID NO: 53; amino acid residues 89-97 of SEQ ID NO: 50)L GACATCCAGATGACCCAGTCTCCATCTTCCGTGTCTGCATCTGTAGGAGACAGAGTCACCATCACTTGTCGGGCGAGTCAGGGTATTAGCAGCTGGTTAGCCTGGTATCAGCAGAAACCAGGGAAAGCCCCTAAGCTCCTGATCTATGCTGCATCCAATTTGCAAAGTGGGGTCCCATCAAGGTTCAGCGGCAGTGGATCTGGGACAGATTTCACTCTCACCATCAGCAGCCTGCAGCCTGAAGATTTTGCAACTTATTACTGTCAGCAGGCACCCGACCTCCCTATCACTTTTGGCGGAGGGACCAAGGTTGAGATCAAACGTACGGTGGCTGCACCTTCCGTCTTTATCTTTCCACCTTCCGATGAGCAGCTGAAGAGCGGAACAGCAAGCGTGGTGTGTCTGCTGAACAACTTTTATCCCCGGGAGGCAAAGGTGCAGTGGAAAGTCGACAATGCTCTCCAGTCCGGCAATTCCCAAGAGAGCGTGACAGAGCAAGATTCCAAGGACTCCACTTACAGCCTGTCCAGCACCCTCACACTGAGCAAGGCTGATTACGAGAAACACAAAGTGTACGCTTGTGAAGTCACCCACCAAGGCCTGAGCAGCCCAGTCACTAAGTCCTTTAACCGGGGCGAATGT (SEQ ID NO: 54) LDIQMTQSPSSVSASVGDRVTITCRASQGISSWLAWYQQKPGKAPKLLIYAASNLQSGVPSRFSGSGSGTDFTLTISSLQPEDFATYYCQQAPDLPITFGGGTKVEIKRTVAAPSVFIFPPSDEQLKSGTASVVCLLNNFYPREAKVQWKVDNALQSGNSQESVFEQDSKDSTYSLSSTLTLSKADYEKHKVYACEVTHQGLSSPVTKSFNRGEC (SEQ ID NO: 55) H01 VHCAGGTGCAGCTGCAGGAGTCGGGCCCAGGACTGGTGAAGCCTTCGGAGACCCTGTCCCTCACCTGCGCTGTCTCTGGTTACTCCATCAGCAGTGGTGTTTACTGGATGTGGATCCGGCAGCCCCCAGGGAAGGGGCTGGAGTGGATTGGGAGTATCGTTCATAGTGGGCATACCTACTACAACCCGTCCCTCAAGAGTCGAGTCACCATATCAGTAGACACGTCCAAGAACCAGTTCTCCCTGAAGCTGAGTTCTGTGACCGCCGCAGACACGGCGGTGTACTACTGCGCCAGAGCTGGAAAATACCGATGGCACGGAATGGACGTATGGGGCCAGGGAACAACTGTCACCGTCTCCTCA (SEQ ID NO: 56) VHQVQLQESGPGLVKPSETLSLTCAVSGYSISSGVYWMWIRQPPGKGLEWIGSIVHSGHTYYNPSLKSRVTISVDTSKNQFSLKLSSVTAADTAVYYCARAGKYRWHGMDVWGQGTTVTVSS (SEQ ID NO: 57)CRD1: GYSISSGV (SEQ ID NO: 58; amino acid residues 26-33 of SEQ ID NO: 57)CDR2: VHSGH (SEQ ID NO: 59; amino acid residues 53-57 of SEQ ID NO: 57)CDR3: AGKYRWHGMDV (SEQ ID NO: 46; amino acid residues 99-109 of SEQ ID NO: 57)H CAGGTGCAGCTGCAGGAGTCGGGCCCAGGACTGGTGAAGCCTTCGGAGACCCTGTCCCTCACCTGCGCTGTCTCTGGTTACTCCATCAGCAGTGGTGTTTACTGGATGTGGATCCGGCAGCCCCCAGGGAAGGGGCTGGAGTGGATTGGGAGTATCGTTCATAGTGGGCATACCTACTACAACCCGTCCCTCAAGAGTCGAGTCACCATATCAGTAGACACGTCCAAGAACCAGTTCTCCCTGAAGCTGAGTTCTGTGACCGCCGCAGACACGGCGGTGTACTACTGCGCCAGAGCTGGAAAATACCGATGGCACGGAATGGACGTATGGGGCCAGGGAACAACTGTCACCGTCTCCTCAGCTAGCACAAAAGGACCAAGCGTGTTTCCACTGGCACCTAGCAGCAAATCCACCAGCGGCGGAACAGCAGCCCTCGGGTGCCTGGTGAAGGATTACTTCCCTGAGCCAGTCACAGTGTCCTGGAACTCCGGAGCCCTGACATCCGGCGTGCACACCTTCCCCGCTGTGCTGCAATCCAGCGGACTGTATAGCCTCAGCTCCGTCGTGACAGTCCCTTCCAGCAGCCTGGGCACACAGACTTACATTTGCAACGTGAACCACAAACCTTCCAACACTAAGGTGGACAAAAAGGTGGAACCCAAATCCTGTGATAAGACCCATACATGCCCACCTTGTCCCGCTCCTGAGCTGCTGGGGGGACCTTCCGTCTTTCTGTTTCCTCCAAAACCAAAAGACACACTCATGATCAGCCGGACCCCCGAAGTCACCTGTGTGGTGGTGGACGTCAGCCACGAAGATCCAGAGGTCAAGTTCAATTGGTACGTGGATGGAGTGGAAGTCCACAACGCAAAAACCAAACCTAGAGAAGAACAGTACAATAGCACATACAGGGTGGTGTCCGTCCTGACAGTGCTCCACCAGGACTGGCTCAATGGCAAAGAGTATAAGTGCAAGGTGAGCAACAAGGCCCTGCCTGCACCAATTGAGAAAACAATTAGCAAGGCAAAGGGGCAGCCACGGGAACCCCAGGTGTATACCCTGCCCCCAAGCCGGGATGAACTGACCAAAAACCAGGTCAGCCTGACATGCCTGGTGAAAGGGTTTTACCCAAGCGATATTGCCGTCGAGTGGGAGAGCAACGGACAGCCAGAAAACAATTACAAAACCACCCCACCTGTGCTGGACTCCGATGGGAGCTTTTTCCTGTACAGCAAGCTCACAGTGGACAAGTCCAGATGGCAACAGGGCAACGTGTTTTCCTGCTCCGTGATGCACGAGGCCCTCCACAACCACTATACACAAAAGTCCCTCTCCCTCAGCCCAGGAAAG (SEQ ID NO: 60) HQVQLQESGPGLVKPSETLSLTCAVSGYSISSGVYWMWIRQPPGKGLEWIGSIVHSGHTYYNPSLKSRVTISVDTSKNQFSLKLSSVTAADTAVYYCARAGKYRWHGMDVWGQGTTVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSVFLEPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFELYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO: 61) VL SEQ ID NO: 49 VLDIQMTQSPSSVSASVGDRVTITCRASQGISSWLAWYQQKPGKAPKLLIYAASNLQSGVPSRFSGSGSGTDFTLTISSLQPEDFATYYCQQAPDLPITFGGGTKVEIK (SEQ ID NO: 50)CDR1: RASQGISSWLA (SEQ ID NO: 51; amino acid residues 24-34 of SEQ ID NO: 50)CDR2: AASNLQS (SEQ ID NO: 52; amino acid residues 50-56 of SEQ ID NO: 50)CDR3: QQAPDLPIT (SEQ ID NO: 53; amino acid residues 89-97 of SEQ ID NO: 50)L SEQ ID NO: 54 L SEQ ID NO: 55 E02 VHGAGGTGCAGCTGTTGGAGTCTGGGGGAGGCTTGGTACAGCCTGGGGGGTCCCTGAGACTCTCCTGTGCAGCCTCTGGATTCACCTTTAGCAGCTATGCCATGAGCTGGGTCCGCCAGGCTCCAGGGAAGGGGCTGGAGTGGGTCTCAGGAATTAGTGGTAGTGGTGGTAGCACATACTACGCAGACTCCGTGAAGGGCCGGTTCACCATCTCCAGAGACAATTCCAAGAACACGCTGTATCTGCAAATGAACAGCCTGAGAGCCGAGGACACGGCGGTGTACTACTGCGCCAAGGACCCTTTGTCTCTACTTCTAGGCTACTTTGACTACTGGGGACAGGGTGCATTGGTCACCGTCTCCTCA (SEQ ID NO: 62) VHEVQLLESGGGLVQPGGSLRLSCAASGFTFSSYAMSWVRQAPGKGLEWVSGISGSGGSTYYADSVKGRFTISRDNSKNTLYLQMNSLRAEDTAVYYCAKD PLSLLLGYFDYWGQGALVTVSS (SEQ ID NO: 63)CDR1: GFTFSSY (SEQ ID NO: 64; amino acid residues 26-32 of SEQ ID NO: 63)CDR2: SGSGGS (SEQ ID NO: 65; amino acid residues 52-57 of SEQ ID NO: 63)CDR3: DPLSLLLGYFDY (SEQ ID NO: 66; amino acid residues 99-110 of SEQ ID NO: 63)H GAGGTGCAGCTGTTGGAGTCTGGGGGAGGCTTGGTACAGCCTGGGGGGTCCCTGAGACTCTCCTGTGCAGCCTCTGGATTCACCTTTAGCAGCTATGCCATGAGCTGGGTCCGCCAGGCTCCAGGGAAGGGGCTGGAGTGGGTCTCAGGAATTAGTGGTAGTGGTGGTAGCACATACTACGCAGACTCCGTGAAGGGCCGGTTCACCATCTCCAGAGACAATTCCAAGAACACGCTGTATCTGCAAATGAACAGCCTGAGAGCCGAGGACACGGCGGTGTACTACTGCGCCAAGGACCCTTTGTCTCTACTTCTAGGCTACTTTGACTACTGGGGACAGGGTGCATTGGTCACCGTCTCCTCAGCTAGCACAAAAGGACCAAGCGTGTTTCCACTGGCACCTAGCAGCAAATCCACCAGCGGCGGAACAGCAGCCCTCGGGTGCCTGGTGAAGGATTACTTCCCTGAGCCAGTCACAGTGTCCTGGAACTCCGGAGCCCTGACATCCGGCGTGCACACCTTCCCCGCTGTGCTGCAATCCAGCGGACTGTATAGCCTCAGCTCCGTCGTGACAGTCCCTTCCAGCAGCCTGGGCACACAGACTTACATTTGCAACGTGAACCACAAACCTTCCAACACTAAGGTGGACAAAAAGGTGGAACCCAAATCCTGTGATAAGACCCATACATGCCCACCTTGTCCCGCTCCTGAGCTGCTGGGGGGACCTTCCGTCTTTCTGTTTCCTCCAAAACCAAAAGACACACTCATGATCAGCCGGACCCCCGAAGTCACCTGTGTGGTGGTGGACGTCAGCCACGAAGATCCAGAGGTCAAGTTCAATTGGTACGTGGATGGAGTGGAAGTCCACAACGCAAAAACCAAACCTAGAGAAGAACAGTACAATAGCACATACAGGGTGGTGTCCGTCCTGACAGTGCTCCACCAGGACTGGCTCAATGGCAAAGAGTATAAGTGCAAGGTGAGCAACAAGGCCCTGCCTGCACCAATTGAGAAAACAATTAGCAAGGCAAAGGGGCAGCCACGGGAACCCCAGGTGTATACCCTGCCCCCAAGCCGGGATGAACTGACCAAAAACCAGGTCAGCCTGACATGCCTGGTGAAAGGGTTTTACCCAAGCGATATTGCCGTCGAGTGGGAGAGCAACGGACAGCCAGAAAACAATTACAAAACCACCCCACCTGTGCTGGACTCCGATGGGAGCTTTTTCCTGTACAGCAAGCTCACAGTGGACAAGTCCAGATGGCAACAGGGCAACGTGTTTTCCTGCTCCGTGATGCACGAGGCCCTCCACAACCACTATACACAAAAGTCCCTCTCCCTCAGCCCAGGAAAG (SEQ ID NO: 67) HEVQLLESGGGLVQPGGSLRLSCAASGFTFSSYAMSWVRQAPGKGLEWVSGISGSGGSTYYADSVKGRFTISRDNSKNTLYLQMNSLRAEDTAVYYCAKDPLSLLLGYFDYWGQGALVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNVVYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO: 68) VLGACATCCAGATGACCCAGTCTCCTTCCACCCTGTCTGCATCTGTAGGAGACAGAGTCACCATCACTTGCCGGGCCAGTCAGAGTATTAGTAGCTGGTTGGCCTGGTATCAGCAGAAACCAGGGAAAGCCCCTAAGCTCCTGATCTATGATGCCTCCAGTTTGGAAAGTGGGGTCCCATCAAGGTTCAGCGGCAGTGGATCTGGGACAGAATTCACTCTCACCATCAGCAGCCTGCAGCCTGATGATTTTGCAACTTATTACTGCCAGCAGTACAATCGCCACTCTCCTACTTTTGGCGGAGGGACCAAGGTTGAGATCAAA (SEQ ID NO: 69) VLDIQMTQSPSTLSASVGDRVTITCRASQSISSWLAWYQQKPGKAPKLLIYDASSLESGVPSRFSGSGSGTEFTLTISSLQPDDFATYYCQQYNRHSPTFGGGTKVEIK (SEQ ID NO: 70)CDR1: RASQSISSWLA (SEQ ID NO: 71; amino acid residues 24-34 of SEQ ID NO: 70)CDR2: DASSLES (SEQ ID NO: 72; amino acid residues 50-56 of SEQ ID NO: 70)CDR3: QQYNRHSPT (SEQ ID NO: 73; amino acid residues 89-97 of SEQ ID NO: 70)L GACATCCAGATGACCCAGTCTCCTTCCACCCTGTCTGCATCTGTAGGAGACAGAGTCACCATCACTTGCCGGGCCAGTCAGAGTATTAGTAGCTGGTTGGCCTGGTATCAGCAGAAACCAGGGAAAGCCCCTAAGCTCCTGATCTATGATGCCTCCAGTTTGGAAAGTGGGGTCCCATCAAGGTTCAGCGGCAGTGGATCTGGGACAGAATTCACTCTCACCATCAGCAGCCTGCAGCCTGATGATTTTGCAACTTATTACTGCCAGCAGTACAATCGCCACTCTCCTACTTTTGGCGGAGGGACCAAGGTTGAGATCAAACGTACGGTGGCTGCACCTTCCGTCTTTATCTTTCCACCTTCCGATGAGCAGCTGAAGAGCGGAACAGCAAGCGTGGTGTGTCTGCTGAACAACTTTTATCCCCGGGAGGCAAAGGTGCAGTGGAAAGTCGACAATGCTCTCCAGTCCGGCAATTCCCAAGAGAGCGTGACAGAGCAAGATTCCAAGGACTCCACTTACAGCCTGTCCAGCACCCTCACACTGAGCAAGGCTGATTACGAGAAACACAAAGTGTACGCTTGTGAAGTCACCCACCAAGGCCTGAGCAGCCCAGTCACTAAGTCCTTTAACCGGGGCGAATGT (SEQ ID NO: 74) LDIQMTQSPSTLSASVGDRVTITCRASQSISSWLAWYQQKPGKAPKLLIYDASSLESGVPSRFSGSGSGTEFTLTISSLQPDDFATYYCQQYNRHSPTFGGGTKVEIKRTVAAPSVFIFPPSDEQLKSGTASVVCLLNNFYPREAKVQWKVDNALQSGNSQESVFEQDSKDSTYSLSSTLTLSKADYEKHKVYACEVTHQGLSSPVTKSFNRGEC (SEQ ID NO: 75) F02 VHGAGGTGCAGCTGTTGGAGTCTGGGGGAGGCTTGGTACAGCCTGGGGGGTCCCTGAGACTCTCCTGTGCAGCCTCTGGATTCACCTTTAGCCGTTATGCCATGTCGTGGGTCCGCCAGGCTCCAGGGAAGGGGCTGGAGTGGGTCTCAGGTATTAGTGGAAGTGGTGGTGCGACATACTACGCAGACTCCGTGAAGGGCCGGTTCACCATCTCCAGAGACAATTCCAAGAACACGCTGTATCTGCAAATGAACAGCCTGAGAGCCGAGGACACGGCGGTGTACTACTGCGCCAAGGACCCTTTGTCTCTACTTCTAGGCTACTTTGACTACTGGGGACAGGGTGCATTGGTCACCGTCTCCTCA (SEQ ID NO: 76) VHEVQLLESGGGLVQPGGSLRLSCAASGFTFSRYAMSWVRQAPGKGLEWVSGISGSGGATYYADSVKGRFTISRDNSKNTLYLQMNSLRAEDTAVYYCAKDPLSLLLGYFDYWGQGALVTVSS (SEQ ID NO: 77)CDR1: GFTFSRY (SEQ ID NO: 78; amino acid residues 26-32 of SEQ ID NO: 77)CDR2: SGSGGA (SEQ ID NO: 79; amino acid residues 52-57 of SEQ ID NO: 77)CDR3: DPLSLLLGYFDY (SEQ ID NO: 80; amino acid residues 99-110 of SEQ ID NO: 77)H GAGGTGCAGCTGTTGGAGTCTGGGGGAGGCTTGGTACAGCCTGGGGGGTCCCTGAGACTCTCCTGTGCAGCCTCTGGATTCACCTTTAGCCGTTATGCCATGTCGTGGGTCCGCCAGGCTCCAGGGAAGGGGCTGGAGTGGGTCTCAGGTATTAGTGGAAGTGGTGGTGCGACATACTACGCAGACTCCGTGAAGGGCCGGTTCACCATCTCCAGAGACAATTCCAAGAACACGCTGTATCTGCAAATGAACAGCCTGAGAGCCGAGGACACGGCGGTGTACTACTGCGCCAAGGACCCTTTGTCTCTACTTCTAGGCTACTTTGACTACTGGGGACAGGGTGCATTGGTCACCGTCTCCTCAGCTAGCACAAAAGGACCAAGCGTGTTTCCACTGGCACCTAGCAGCAAATCCACCAGCGGCGGAACAGCAGCCCTCGGGTGCCTGGTGAAGGATTACTTCCCTGAGCCAGTCACAGTGTCCTGGAACTCCGGAGCCCTGACATCCGGCGTGCACACCTTCCCCGCTGTGCTGCAATCCAGCGGACTGTATAGCCTCAGCTCCGTCGTGACAGTCCCTTCCAGCAGCCTGGGCACACAGACTTACATTTGCAACGTGAACCACAAACCTTCCAACACTAAGGTGGACAAAAAGGTGGAACCCAAATCCTGTGATAAGACCCATACATGCCCACCTTGTCCCGCTCCTGAGCTGCTGGGGGGACCTTCCGTCTTTCTGTTTCCTCCAAAACCAAAAGACACACTCATGATCAGCCGGACCCCCGAAGTCACCTGTGTGGTGGTGGACGTCAGCCACGAAGATCCAGAGGTCAAGTTCAATTGGTACGTGGATGGAGTGGAAGTCCACAACGCAAAAACCAAACCTAGAGAAGAACAGTACAATAGCACATACAGGGTGGTGTCCGTCCTGACAGTGCTCCACCAGGACTGGCTCAATGGCAAAGAGTATAAGTGCAAGGTGAGCAACAAGGCCCTGCCTGCACCAATTGAGAAAACAATTAGCAAGGCAAAGGGGCAGCCACGGGAACCCCAGGTGTATACCCTGCCCCCAAGCCGGGATGAACTGACCAAAAACCAGGTCAGCCTGACATGCCTGGTGAAAGGGTTTTACCCAAGCGATATTGCCGTCGAGTGGGAGAGCAACGGACAGCCAGAAAACAATTACAAAACCACCCCACCTGTGCTGGACTCCGATGGGAGCTTTTTCCTGTACAGCAAGCTCACAGTGGACAAGTCCAGATGGCAACAGGGCAACGTGTTTTCCTGCTCCGTGATGCACGAGGCCCTCCACAACCACTATACACAAAAGTCCCTCTCCCTCAGCCCAGGAAAG (SEQ ID NO: 81) HEVQLLESGGGLVQPGGSLRLSCAASGFTESRYAMSWVRQAPGKGLEWVSGISGSGGATYYADSVKGRFTISRDNSKNTLYLQMNSLRAEDTAVYYCAKDPLSLLLGYFDYWGQGALVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSVFLEPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKENWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFELYSKLTVDKSRWQQGNVESCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO: 82) VLSEQ ID NO: 69 VLDIQMTQSPSTLSASVGDRVTITCRASQSISSWLAWYQQKPGKAPKLLIYDASSLESGVPSRFSGSGSGTEFTLTISSLQPDDFATYYCQQYNRHSPTFGGGTKVEIK (SEQ ID NO: 70)CDR1: RASQSISSWLA (SEQ ID NO: 71; amino acid residues 24-34 of SEQ ID NO: 70)CDR2: DASSLES (SEQ ID NO: 72; amino acid residues 50-56 of SEQ ID NO: 70)CDR3: QQYNRHSPT (SEQ ID NO: 73; amino acid residues 89-97 of SEQ ID NO: 70)L SEQ ID NO: 74 L SEQ ID NO: 75 I01 VHGAGGTGCAGCTGTTGGAGTCTGGGGGAGGCTTGGTACAGCCTGGGGGGTCCCTGAGACTCTCCTGTGCAGCCTCTGGATTCACCTTTGGGAGCTATGGCATGACTTGGGTCCGCCAGGCTCCAGGGAAGGGGCTGGAGTGGGTCTCAGTTATTAGTGGAAGTGGTGGTGGGACATACTACGCAGACTCCGTGAAGGGCCGGTTCACCATCTCCAGAGACAATTCCAAGAACACGCTGTATCTGCAAATGAACAGCCTGAGAGCCGAGGACACGGCGGTGTACTACTGCGCCAAGGGTCCTAGAATAGTGGGCATGGATGTGTGGGGCCAGGGAACAACTGTCACCGTCTCCTCA (SEQ ID NO: 143) VHEVQLLESGGGLVQPGGSLRLSCAASGFTFGSYGMTWVRQAPGKGLEWVSVISGSGGGTYYADSVKGRFTISRDNSKNTLYLQMNSLRAEDTAVYYCAKGPRIVGMDVWGQGTTVTVS (SEQ ID NO: 144)CDR1: SYGMT (SEQ ID NO: 145; amino acid residues 31-35 of SEQ ID NO: 144)CDR2: VISGSGGGTYYADSVKG (SEQ ID NO: 146; amino acid residues 50-65 of SEQ ID NO: 144)CDR3: GPRIVGMDV (SEQ ID NO: 147; amino acid residues 95-102 of SEQ ID NO: 144)H GAGGTGCAGCTGTTGGAGTCTGGGGGAGGCTTGGTACAGCCTGGGGGGTCCCTGAGACTCTCCTGTGCAGCCTCTGGATTCACCTTTGGGAGCTATGGCATGACTTGGGTCCGCCAGGCTCCAGGGAAGGGGCTGGAGTGGGTCTCAGTTATTAGTGGAAGTGGTGGTGGGACATACTACGCAGACTCCGTGAAGGGCCGGTTCACCATCTCCAGAGACAATTCCAAGAACACGCTGTATCTGCAAATGAACAGCCTGAGAGCCGAGGACACGGCGGTGTACTACTGCGCCAAGGGTCCTAGAATAGTGGGCATGGATGTGTGGGGCCAGGGAACAACTGTCACCGTCTCCTCAGCTTCCACCAAGGGCCCATCCGTCTTCCCCCTGGCGCCCTGCTCCAGGAGCACCTCCGAGAGCACAGCCGCCCTGGGCTGCCTGGTCAAGGACTACTTCCCCGAACCGGTGACGGTGTCGTGGAACTCAGGCGCCCTGACCAGCGGCGTGCACACCTTCCCGGCTGTCCTACAGTCCTCAGGACTCTACTCCCTCAGCAGCGTGGTGACCGTGCCCTCCAGCAGCTTGGGCACGAAGACCTACACCTGCAACGTAGATCACAAGCCCAGCAACACCAAGGTGGACAAGAGAGTTGAGTCCAAATATGGTCCCCCATGCCCACCCTGCCCAGCACCTGAGTTCCTGGGGGGACCATCAGTCTTCCTGTTCCCCCCAAAACCCAAGGACACTCTCATGATCTCCCGGACCCCTGAGGTCACGTGCGTGGTGGTGGACGTGAGCCAGGAAGACCCCGAGGTCCAGTTCAACTGGTACGTGGATGGCGTGGAGGTGCATAATGCCAAGACAAAGCCGCGGGAGGAGCAGTTCAACAGCACGTACCGTGTGGTCAGCGTCCTCACCGTCCTGCACCAGGACTGGCTGAACGGCAAGGAGTACAAGTGCAAGGTCTCCAACAAAGGCCTCCCGTCCTCCATCGAGAAAACCATCTCCAAAGCCAAAGGGCAGCCCCGAGAGCCACAGGTGTACACCCTGCCCCCATCCCAGGAGGAGATGACCAAGAACCAGGTCAGCCTGACCTGCCTGGTCAAAGGCTTCTACCCCAGCGACATCGCCGTGGAGTGGGAGAGCAATGGGCAGCCGGAGAACAACTACAAGACCACGCCTCCCGTGCTGGACTCCGACGGCTCCTTCTTCCTCTACAGCAGGCTAACCGTGGACAAGAGCAGGTGGCAGGAGGGGAATGTCTTCTCATGCTCCGTGATGCATGAGGCTCTGCACAACCACTACACACAGAAGAGCCTCTCCCTGTCTCTGGGTAAATGA (SEQ ID NO: 148) HEVQLLESGGGLVQPGGSLRLSCAASGETEGSYGMTWVRQAPGKGLEWVSVISGSGGGTYYADSVKGRFTISRDNSKNTLYLQMNSLRAEDTAVYYCAKGPRIVGMDVWGQGTTVTVSSASTKGPSVFPLAPCSRSTSESTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSSSLGTKTYTCNVDHKPSNTKVDKRVESKYGPPCPPCPAPEFLGGPSVFLEPPKPKDTLMISRTPEVTCVVVDVSQEDPEVQFNWYVDGVEVHNAKTKPREEQFNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKGLPSSIEKTISKAKGQPREPQVYTLPPSQEEMTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFELYSRLTVDKSRWQEGNVFSCSVMHEALHNHYTQKSLSLSLGK (SEQ ID NO: 149) VLGACATCCAGATGACCCAGTCTCCATCTTCCGTGTCTGCATCTGTAGGAGACAGAGTCACCATCACTTGTCGGGCGAGTCAGGGTATTAGCAGCTGGTTAGCCTGGTATCAGCAGAAACCAGGGAAAGCCCCTAAGCTCCTGATCTATGCTGCATCCAGTTTGCAAAGTGGGGTCCCATCAAGGTTCAGCGGCAGTGGATCTGGGACAGATTTCACTCTCACCATCAGCAGCCTGCAGCCTGAAGATTTTGCAACTTATTACTGTCAGCAGGTATTCAGTTACCCTCTCACTTTTGGCGGAGGGACCAAGGTTGAGATCAAA (SEQ ID NO: 150) VLDIQMTQSPSSVSASVGDRVTITCRASQGISSWLAWYQQKPGKAPKLLIYAASSLQSGVPSRFSGSGSGTDFTLTISSLQPEDFATYYCQQVFSYPLTFGGGTKVEIK (SEQ ID NO: 151)CDR1: RASQGISSWLA (SEQ ID NO: 152; amino acid residues 24-34 of SEQ ID NO: 151)CDR2: AASSLQS (SEQ ID NO: 153; amino acid residues 50-56 of SEQ ID NO: 151)CDR3: QQVFSYPLT (SEQ ID NO: 154; amino acid residues 89-97 of SEQ ID NO: 151)L GACATCCAGATGACCCAGTCTCCATCTTCCGTGTCTGCATCTGTAGGAGACAGAGTCACCATCACTTGTCGGGCGAGTCAGGGTATTAGCAGCTGGTTAGCCTGGTATCAGCAGAAACCAGGGAAAGCCCCTAAGCTCCTGATCTATGCTGCATCCAGTTTGCAAAGTGGGGTCCCATCAAGGTTCAGCGGCAGTGGATCTGGGACAGATTTCACTCTCACCATCAGCAGCCTGCAGCCTGAAGATTTTGCAACTTATTACTGTCAGCAGGTATTCAGTTACCCTCTCACTTTTGGCGGAGGGACCAAGGTTGAGATCAAACGAACTGTGGCTGCACCATCTGTCTTCATCTTCCCGCCATCTGATGAGCAGTTGAAATCTGGAACTGCCTCTGTTGTGTGCCTGCTGAATAACTTCTATCCCAGAGAGGCCAAAGTACAGTGGAAGGTGGATAACGCCCTCCAATCGGGTAACTCCCAGGAGAGTGTCACAGAGCAGGACAGCAAGGACAGCACCTACAGCCTCAGCAGCACCCTGACGCTGAGCAAAGCAGACTACGAGAAACACAAAGTCTACGCCTGCGAAGTCACCCATCAGGGCCTGAGCTCGCCCGTCACAAAGAGCTTCAACAGGGGAGAGTGTTAG (SEQ ID NO: 155) LDIQMTQSPSSVSASVGDRVTITCRASQGISSWLAWYQQKPGKAPKLLIYAASSLQSGVPSRFSGSGSGTDFTLTISSLQPEDFATYYCQQVFSYPLTFGGGTKVEIKRTVAAPSVFIFPPSDEQLKSGTASVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYACEVTHQGLSSPVTKSFNRGEC (SEQ ID NO: 156) ActRIIB- and ActRIIA--binding Antibodies A02 VHCAGGTTCAGCTGGTGCAGTCTGGAGCTGAGGTGAAGAAGCCTGGGGCCTCAGTGAAGGTCTCCTGCAAGGCTTCTGGTTACACCTTTACCAGCTATGGTATCAGCTGGGTGCGACAGGCCCCTGGACAAGGGCTTGAGTGGATGGGATGGATCAGCCCTTACAATGGTAACACAAACTATGCACAGAAGCTCCAGGGCAGAGTCACCATGACCACAGACACATCCACGAGCACAGCCTACATGGAGCTGAGGAGCCTGAGATCTGACGACACGGCGGTGTACTACTGCGCTAGAGTATCTATGTACGCCCCAGAGCCAATGGACGTATGGGGCCAGGGAACAACTGTCACCGTCTCCTCA (SEQ ID NO: 83) VHQVQLVQSGAEVKKPGASVKVSCKASGYTFTSYGISWVRQAPGQGLEWMGWISPYNGNTNYAQKLQGRVTMTTDTSTSTAYMELRSLRSDDTAVYYCARVSMYAPEPMDVWGQGTTVTVSS (SEQ ID NO: 84)CDR1: GYTFTSY (SEQ ID NO: 85; amino acid residues 26-32 of SEQ ID NO: 84)CDR2: SPYNGN (SEQ ID NO: 86; amino acid residues 52-57 of SEQ ID NO: 84)CDR3: VSMYAPEPMDV (SEQ ID NO: 87; amino acid residues 99-109 of SEQ ID NO: 84)H CAGGTTCAGCTGGTGCAGTCTGGAGCTGAGGTGAAGAAGCCTGGGGCCTCAGTGAAGGTCTCCTGCAAGGCTTCTGGTTACACCTTTACCAGCTATGGTATCAGCTGGGTGCGACAGGCCCCTGGACAAGGGCTTGAGTGGATGGGATGGATCAGCCCTTACAATGGTAACACAAACTATGCACAGAAGCTCCAGGGCAGAGTCACCATGACCACAGACACATCCACGAGCACAGCCTACATGGAGCTGAGGAGCCTGAGATCTGACGACACGGCGGTGTACTACTGCGCTAGAGTATCTATGTACGCCCCAGAGCCAATGGACGTATGGGGCCAGGGAACAACTGTCACCGTCTCCTCAGCTAGCACAAAAGGACCAAGCGTGTTTCCACTGGCACCTAGCAGCAAATCCACCAGCGGCGGAACAGCAGCCCTCGGGTGCCTGGTGAAGGATTACTTCCCTGAGCCAGTCACAGTGTCCTGGAACTCCGGAGCCCTGACATCCGGCGTGCACACCTTCCCCGCTGTGCTGCAATCCAGCGGACTGTATAGCCTCAGCTCCGTCGTGACAGTCCCTTCCAGCAGCCTGGGCACACAGACTTACATTTGCAACGTGAACCACAAACCTTCCAACACTAAGGTGGACAAAAAGGTGGAACCCAAATCCTGTGATAAGACCCATACATGCCCACCTTGTCCCGCTCCTGAGCTGCTGGGGGGACCTTCCGTCTTTCTGTTTCCTCCAAAACCAAAAGACACACTCATGATCAGCCGGACCCCCGAAGTCACCTGTGTGGTGGTGGACGTCAGCCACGAAGATCCAGAGGTCAAGTTCAATTGGTACGTGGATGGAGTGGAAGTCCACAACGCAAAAACCAAACCTAGAGAAGAACAGTACAATAGCACATACAGGGTGGTGTCCGTCCTGACAGTGCTCCACCAGGACTGGCTCAATGGCAAAGAGTATAAGTGCAAGGTGAGCAACAAGGCCCTGCCTGCACCAATTGAGAAAACAATTAGCAAGGCAAAGGGGCAGCCACGGGAACCCCAGGTGTATACCCTGCCCCCAAGCCGGGATGAACTGACCAAAAACCAGGTCAGCCTGACATGCCTGGTGAAAGGGTTTTACCCAAGCGATATTGCCGTCGAGTGGGAGAGCAACGGACAGCCAGAAAACAATTACAAAACCACCCCACCTGTGCTGGACTCCGATGGGAGCTTTTTCCTGTACAGCAAGCTCACAGTGGACAAGTCCAGATGGCAACAGGGCAACGTGTTTTCCTGCTCCGTGATGCACGAGGCCCTCCACAACCACTATACACAAAAGTCCCTCTCCCTCAGCCCAGGAAAG (SEQ ID NO: 88) HQVQLVQSGAEVKKPGASVKVSCKASGYTFTSYGISWVRQAPGQGLEWMGWISPYNGNTNYAQKLQGRVTMTTDTSTSTAYMELRSLRSDDTAVYYCARVSMYAPEPMDVWGQGTTVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO: 89) VLGACATCCAGATGACCCAGTCTCCATCTTCCGTGTCTGCATCTGTAGGAGACAGAGTCACCATCACTTGTCGGGCGAGTCAGGGTATTAGCAGGTGGTTAGCCTGGTATCAGCAGAAACCAGGGAAAGCCCCTAAGCTCCTGATCTATGCTGCATCCAGTTTGCAAAGTGGGGTCCCATCAAGGTTCAGCGGCAGTGGATCTGGGACAGATTTCACTCTCACCATCAGCAGCCTGCAGCCTGAAGATTTTGCAACTTATTACTGTCAGCAGGCATTCTCCCACCCTTGGACTTTTGGCGGAGGGACCAAGGTTGAGATCAAA (SEQ ID NO: 90) VLDIQMTQSPSSVSASVGDRVTITCRASQGISRWLAWYQQKPGKAPKLLIYAASSLQSGVPSRFSGSGSGTDFTLTISSLQPEDFATYYCQQAFSHPWTFGGGTKVEIK (SEQ ID NO: 91)CDR1: RASQGISRWLA (SEQ ID NO: 92; amino acid residues 24-34 of SEQ ID NO: 91)CDR2: ASSLQS (SEQ ID NO: 93; amino acid residues 50-56 of SEQ ID NO: 91)CDR3: QQAFSHPWT (SEQ ID NO: 94; amino acid residues 89-97 of SEQ ID NO: 91)L GACATCCAGATGACCCAGTCTCCATCTTCCGTGTCTGCATCTGTAGGAGACAGAGTCACCATCACTTGTCGGGCGAGTCAGGGTATTAGCAGGTGGTTAGCCTGGTATCAGCAGAAACCAGGGAAAGCCCCTAAGCTCCTGATCTATGCTGCATCCAGTTTGCAAAGTGGGGTCCCATCAAGGTTCAGCGGCAGTGGATCTGGGACAGATTTCACTCTCACCATCAGCAGCCTGCAGCCTGAAGATTTTGCAACTTATTACTGTCAGCAGGCATTCTCCCACCCTTGGACTTTTGGCGGAGGGACCAAGGTTGAGATCAAACGTACGGTGGCTGCACCTTCCGTCTTTATCTTTCCACCTTCCGATGAGCAGCTGAAGAGCGGAACAGCAAGCGTGGTGTGTCTGCTGAACAACTTTTATCCCCGGGAGGCAAAGGTGCAGTGGAAAGTCGACAATGCTCTCCAGTCCGGCAATTCCCAAGAGAGCGTGACAGAGCAAGATTCCAAGGACTCCACTTACAGCCTGTCCAGCACCCTCACACTGAGCAAGGCTGATTACGAGAAACACAAAGTGTACGCTTGTGAAGTCACCCACCAAGGCCTGAGCAGCCCAGTCACTAAGTCCTTTAACCGGGGCGAATGT (SEQ ID NO: 95) LDIQMTQSPSSVSASVGDRVTITCRASQGISRWLAWYQQKPGKAPKLLIYAASSLQSGVPSRFSGSGSGTDFTLTISSLQPEDFATYYCQQAFSHPWTFGGGTKVEIK (SEQ ID NO: 96) B02 VHCAGGTGCAGCTGGTGCAGTCTGGGGCTGAGGTGAAGAAGCCTGGGGCCTCAGTGAAGGTCTCCTGCAAGGCTTCTGGATACACCTTCACCGGCCATAAGATGCACTGGGTGCGACAGGCCCCTGGACAAGGGCTTGAGTGGATGGGATGGATCAACCCTGCTAGTGGTTGGACAAACTATGCACAGAAGTTTCAGGGCAGGGTCACCATGACCAGGGACACGTCCATCAGCACAGCCTACATGGAGCTGAGCAGGCTGAGATCTGACGACACGGCGGTGTACTACTGCGCCAGAGTATCTATGTACGCCCCAGAGCCAATGGACGTATGGGGCCAGGGAACAACTGTCACCGTCTCCTCA (SEQ ID NO: 97) VHQVQLVQSGAEVKKPGASVKVSCKASGYTFTGHKMHWVRQAPGQGLEWMGWINPASGWTNYAQKFQGRVTMTRDTSISTAYMELSRLRSDDTAVYYCARVSMYAPEPMDVWGQGTTVTVSS (SEQ ID NO: 98)CDR1: GYTFTGHKMH (SEQ ID NO: 99; amino acid residues 26-35 of SEQ ID NO: 98)CDR2: NPASGW (SEQ ID NO: 100; amino acid residues 52-57 of SEQ ID NO: 98)CDR3: VSMYAPEPMDV (SEQ ID NO: 101; amino acid residues 99-109 of SEQ ID NO: 98)H CAGGTGCAGCTGGTGCAGTCTGGGGCTGAGGTGAAGAAGCCTGGGGCCTCAGTGAAGGTCTCCTGCAAGGCTTCTGGATACACCTTCACCGGCCATAAGATGCACTGGGTGCGACAGGCCCCTGGACAAGGGCTTGAGTGGATGGGATGGATCAACCCTGCTAGTGGTTGGACAAACTATGCACAGAAGTTTCAGGGCAGGGTCACCATGACCAGGGACACGTCCATCAGCACAGCCTACATGGAGCTGAGCAGGCTGAGATCTGACGACACGGCGGTGTACTACTGCGCCAGAGTATCTATGTACGCCCCAGAGCCAATGGACGTATGGGGCCAGGGAACAACTGTCACCGTCTCCTCAGCTAGCACAAAAGGACCAAGCGTGTTTCCACTGGCACCTAGCAGCAAATCCACCAGCGGCGGAACAGCAGCCCTCGGGTGCCTGGTGAAGGATTACTTCCCTGAGCCAGTCACAGTGTCCTGGAACTCCGGAGCCCTGACATCCGGCGTGCACACCTTCCCCGCTGTGCTGCAATCCAGCGGACTGTATAGCCTCAGCTCCGTCGTGACAGTCCCTTCCAGCAGCCTGGGCACACAGACTTACATTTGCAACGTGAACCACAAACCTTCCAACACTAAGGTGGACAAAAAGGTGGAACCCAAATCCTGTGATAAGACCCATACATGCCCACCTTGTCCCGCTCCTGAGCTGCTGGGGGGACCTTCCGTCTTTCTGTTTCCTCCAAAACCAAAAGACACACTCATGATCAGCCGGACCCCCGAAGTCACCTGTGTGGTGGTGGACGTCAGCCACGAAGATCCAGAGGTCAAGTTCAATTGGTACGTGGATGGAGTGGAAGTCCACAACGCAAAAACCAAACCTAGAGAAGAACAGTACAATAGCACATACAGGGTGGTGTCCGTCCTGACAGTGCTCCACCAGGACTGGCTCAATGGCAAAGAGTATAAGTGCAAGGTGAGCAACAAGGCCCTGCCTGCACCAATTGAGAAAACAATTAGCAAGGCAAAGGGGCAGCCACGGGAACCCCAGGTGTATACCCTGCCCCCAAGCCGGGATGAACTGACCAAAAACCAGGTCAGCCTGACATGCCTGGTGAAAGGGTTTTACCCAAGCGATATTGCCGTCGAGTGGGAGAGCAACGGACAGCCAGAAAACAATTACAAAACCACCCCACCTGTGCTGGACTCCGATGGGAGCTTTTTCCTGTACAGCAAGCTCACAGTGGACAAGTCCAGATGGCAACAGGGCAACGTGTTTTCCTGCTCCGTGATGCACGAGGCCCTCCACAACCACTATACACAAAAGTCCCTCTCCCTCAGCCCAGGAAAG(SEQ ID NO: 102) HQVQLVQSGAEVKKPGASVKVSCKASGYTFTGHKMHWVRQAPGQGLEWMGWINPASGWTNYAQKFQGRVTMTRDTSISTAYMELSRLRSDDTAVYYCARVSMYAPEPMDVWGQGTTVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO: 103) VLSEQ ID NO: 90 VLDIQMTQSPSSVSASVGDRVTITCRASQGISRWLAWYQQKPGKAPKLLIYAASSLQSGVPSRFSGSGSGTDFTLTISSLQPEDFATYYCQQAFSHPWTFGGGTKVEIK (SEQ ID NO: 91)CDR1: RASQGISRWLA (SEQ ID NO: 92; amino acid residues 24-34 of SEQ ID NO: 91)CDR2: AASSLQS (SEQ ID NO: 153; amino acid residues 50-56 of SEQ ID NO: 91)CDR3: QQAFSHPWT (SEQ ID NO: 94; amino acid residues 89-97 of SEQ ID NO: 91)L SEQ ID NO: 95 L SEQ ID NO: 96 C02 VHCAGGTGCAGCTGGTGCAGTCTGGGGCTGAGGTGAAGAAGCCTGGGGCCTCAGTGAAGGTTTCCTGCAAGGCATCTGGATACACCTTCACCAGCTACAATATGGCGTGGGTGCGACAGGCCCCTGGACAAGGGCTTGAGTGGATGGGAATAATCAGGCCTAGTGTTGGTAGCACAAGCTACGCACAGAAGTTCCAGGGCAGAGTCACCATGACCAGGGACACGTCCACGAGCACAGTCTACATGGAGCTGAGCAGCCTGAGATCTGAGGACACGGCGGTGTACTACTGCGCTAGAGTATCTATGTACGCCCCAGAGCCAATGGACGTATGGGGCCAGGGAACAACTGTCACCGTCTCCTCA (SEQ ID NO: 104) VHQVQLVQSGAEVKKPGASVKVSCKASGYTFTSYNMAWVRQAPGQGLEWMGIIRPSVGSTSYAQKFQGRVTMTRDTSTSTVYMELSSLRSEDTAVYYCARVSMYAPEPMDVWGQGTTVTVSS (SEQ ID NO: 105)CDR1: GYTFTSY (SEQ ID NO: 106; amino acid residues 26-32 of SEQ ID NO: 105)CDR2: RPSVGS (SEQ ID NO: 107; amino acid residues 52-57 of SEQ ID NO: 105)CDR3: VSMYAPEPMDV (SEQ ID NO: 108; amino acid residues 99-109 of SEQ ID NO: 105)H CAGGTGCAGCTGGTGCAGTCTGGGGCTGAGGTGAAGAAGCCTGGGGCCTCAGTGAAGGTTTCCTGCAAGGCATCTGGATACACCTTCACCAGCTACAATATGGCGTGGGTGCGACAGGCCCCTGGACAAGGGCTTGAGTGGATGGGAATAATCAGGCCTAGTGTTGGTAGCACAAGCTACGCACAGAAGTTCCAGGGCAGAGTCACCATGACCAGGGACACGTCCACGAGCACAGTCTACATGGAGCTGAGCAGCCTGAGATCTGAGGACACGGCGGTGTACTACTGCGCTAGAGTATCTATGTACGCCCCAGAGCCAATGGACGTATGGGGCCAGGGAACAACTGTCACCGTCTCCTCAGCTAGCACAAAAGGACCAAGCGTGTTTCCACTGGCACCTAGCAGCAAATCCACCAGCGGCGGAACAGCAGCCCTCGGGTGCCTGGTGAAGGATTACTTCCCTGAGCCAGTCACAGTGTCCTGGAACTCCGGAGCCCTGACATCCGGCGTGCACACCTTCCCCGCTGTGCTGCAATCCAGCGGACTGTATAGCCTCAGCTCCGTCGTGACAGTCCCTTCCAGCAGCCTGGGCACACAGACTTACATTTGCAACGTGAACCACAAACCTTCCAACACTAAGGTGGACAAAAAGGTGGAACCCAAATCCTGTGATAAGACCCATACATGCCCACCTTGTCCCGCTCCTGAGCTGCTGGGGGGACCTTCCGTCTTTCTGTTTCCTCCAAAACCAAAAGACACACTCATGATCAGCCGGACCCCCGAAGTCACCTGTGTGGTGGTGGACGTCAGCCACGAAGATCCAGAGGTCAAGTTCAATTGGTACGTGGATGGAGTGGAAGTCCACAACGCAAAAACCAAACCTAGAGAAGAACAGTACAATAGCACATACAGGGTGGTGTCCGTCCTGACAGTGCTCCACCAGGACTGGCTCAATGGCAAAGAGTATAAGTGCAAGGTGAGCAACAAGGCCCTGCCTGCACCAATTGAGAAAACAATTAGCAAGGCAAAGGGGCAGCCACGGGAACCCCAGGTGTATACCCTGCCCCCAAGCCGGGATGAACTGACCAAAAACCAGGTCAGCCTGACATGCCTGGTGAAAGGGTTTTACCCAAGCGATATTGCCGTCGAGTGGGAGAGCAACGGACAGCCAGAAAACAATTACAAAACCACCCCACCTGTGCTGGACTCCGATGGGAGCTTTTTCCTGTACAGCAAGCTCACAGTGGACAAGTCCAGATGGCAACAGGGCAACGTGTTTTCCTGCTCCGTGATGCACGAGGCCCTCCACAACCACTATACACAAAAGTCCCTCTCCCTCAGCCCAGGAAAG (SEQ ID NO: 109) HQVQLVQSGAEVKKPGASVKVSCKASGYTFTSYNMAWVRQAPGQGLEWMGIIRPSVGSTSYAQKFQGRVTMTRDTSTSTVYMELSSLRSEDTAVYYCARVSMYAPEPMDVWGQGTTVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO: 110) VLSEQ ID NO: 90 VLDIQMTQSPSSVSASVGDRVTITCRASQGISRWLAWYQQKPGKAPKLLIYAASSLQSGVPSRFSGSGSGTDFTLTISSLQPEDFATYYCQQAFSHPWTFGGGTKVEIK (SEQ ID NO: 91)CDR1: RASQGISRWLA (SEQ ID NO: 92; amino acid residues 24-34 of SEQ ID NO: 91)CDR2: AASSLQS (SEQ ID NO: 153; amino acid residues 50-56 of SEQ ID NO: 91)CDR3: QQAFSHPWT (SEQ ID NO: 94; amino acid residues 89-97 of SEQ ID NO: 91)L SEQ ID NO: 95 L SEQ ID NO: 96 D02 VHCAGGTGCAGCTGGTGCAGTCTGGGGCTGAGGTGAAGAAGCCTGGGGCCTCAGTGAAGGTTTCCTGCAAGGCATCTGGATACACCTTCACCTCGTACCGTATGCACTGGGTGCGACAGGCCCCTGGACAAGGGCTTGAGTGGATGGGATTTATCGTGCCTAGTGGTGGTAGCACAAGCTACGCACAGAAGTTCCAGGGCAGAGTCACCATGACCAGGGACACGTCCACGAGCACAGTCTACATGGAGCTGAGCAGCCTGAGATCTGAGGACACGGCGGTGTACTACTGCGCTAGAGTATCTATGTACGCCCCAGAGCCAATGGACGTATGGGGCCAGGGAACAACTGTCACCGTCTCCTCA (SEQ ID NO: 111) VHQVQLVQSGAEVKKPGASVKVSCKASGYTFTSYRMHWVRQAPGQGLEWMGFIVPSGGSTSYAQKFQGRVTMTRDTSTSTVYMELSSLRSEDTAVYYCARVSMYAPEPMDVWGQGTTVTVSS (SEQ ID NO: 112)CDR1: GYTFTSY (SEQ ID NO: 113; amino acid residues 26-32 of SEQ ID NO: 112)CDR2: VPSGGS (SEQ ID NO: 114; amino acid residues 52-57 of SEQ ID NO: 112)CDR3: VSMYAPEPMDV (SEQ ID NO: 115; amino acid residues 99-109 of SEQ ID NO: 112)H CAGGTGCAGCTGGTGCAGTCTGGGGCTGAGGTGAAGAAGCCTGGGGCCTCAGTGAAGGTTTCCTGCAAGGCATCTGGATACACCTTCACCTCGTACCGTATGCACTGGGTGCGACAGGCCCCTGGACAAGGGCTTGAGTGGATGGGATTTATCGTGCCTAGTGGTGGTAGCACAAGCTACGCACAGAAGTTCCAGGGCAGAGTCACCATGACCAGGGACACGTCCACGAGCACAGTCTACATGGAGCTGAGCAGCCTGAGATCTGAGGACACGGCGGTGTACTACTGCGCTAGAGTATCTATGTACGCCCCAGAGCCAATGGACGTATGGGGCCAGGGAACAACTGTCACCGTCTCCTCAGCTAGCACAAAAGGACCAAGCGTGTTTCCACTGGCACCTAGCAGCAAATCCACCAGCGGCGGAACAGCAGCCCTCGGGTGCCTGGTGAAGGATTACTTCCCTGAGCCAGTCACAGTGTCCTGGAACTCCGGAGCCCTGACATCCGGCGTGCACACCTTCCCCGCTGTGCTGCAATCCAGCGGACTGTATAGCCTCAGCTCCGTCGTGACAGTCCCTTCCAGCAGCCTGGGCACACAGACTTACATTTGCAACGTGAACCACAAACCTTCCAACACTAAGGTGGACAAAAAGGTGGAACCCAAATCCTGTGATAAGACCCATACATGCCCACCTTGTCCCGCTCCTGAGCTGCTGGGGGGACCTTCCGTCTTTCTGTTTCCTCCAAAACCAAAAGACACACTCATGATCAGCCGGACCCCCGAAGTCACCTGTGTGGTGGTGGACGTCAGCCACGAAGATCCAGAGGTCAAGTTCAATTGGTACGTGGATGGAGTGGAAGTCCACAACGCAAAAACCAAACCTAGAGAAGAACAGTACAATAGCACATACAGGGTGGTGTCCGTCCTGACAGTGCTCCACCAGGACTGGCTCAATGGCAAAGAGTATAAGTGCAAGGTGAGCAACAAGGCCCTGCCTGCACCAATTGAGAAAACAATTAGCAAGGCAAAGGGGCAGCCACGGGAACCCCAGGTGTATACCCTGCCCCCAAGCCGGGATGAACTGACCAAAAACCAGGTCAGCCTGACATGCCTGGTGAAAGGGTTTTACCCAAGCGATATTGCCGTCGAGTGGGAGAGCAACGGACAGCCAGAAAACAATTACAAAACCACCCCACCTGTGCTGGACTCCGATGGGAGCTTTTTCCTGTACAGCAAGCTCACAGTGGACAAGTCCAGATGGCAACAGGGCAACGTGTTTTCCTGCTCCGTGATGCACGAGGCCCTCCACAACCACTATACACAAAAGTCCCTCTCCCTCAGCCCAGGAAAG (SEQ ID NO: 116) HQVQLVQSGAEVKKPGASVKVSCKASGYTFTSYRMHWVRQAPGQGLEWMGFIVPSGGSTSYAQKFQGRVTMTRDTSTSTVYMELSSLRSEDTAVYYCARVSMYAPEPMDVWGQGTTVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO: 117) VLSEQ ID NO: 90 VLDIQMTQSPSSVSASVGDRVTITCRASQGISRWLAWYQQKPGKAPKLLIYAASSLQSGVPSRFSGSGSGTDFTLTISSLQPEDFATYYCQQAFSHPWTFGGGTKVEIK (SEQ ID NO: 91)CDR1: RASQGISRWLA (SEQ ID NO: 92; amino acid residues 24-34 of SEQ ID NO: 91)CDR2: AASSLQS (SEQ ID NO: 153; amino acid residues 50-56 of SEQ ID NO: 91)CDR3: QQAFSHPWT (SEQ ID NO: 94; amino acid residues 89-97 of SEQ ID NO: 91)L SEQ ID NO: 95 L SEQ ID NO: 96 D03 VHCAGGTGCAGCTGGTGCAGTCTGGGGCTGAGGTGAAGAAGCCTGGGGCCTCAGTGAAGGTTTCCTGCAAGGCATCTGGATACACCTTCACCTCGTACCGTATGCACTGGGTGCGACAGGCCCCTGGACAAGGGCTTGAGTGGATGGGATTTATCGTGCCTAGTGGTGGTAGCACAGGCTACGCACAGAAGTTCCAGGGCAGAGTTACCATGACCAGGGACACGTCCACGAGCACAGTCTACATGGAGCTGAGCAGCCTGAGATCTGAGGACACGGCGGTGTACTACTGCGCTAGAGTATCTAGGTACGCCCCAGAGCCAATGGACGTATGGGGCCAGGGAACAACTGTCACCGTCTCCTCA (SEQ ID NO: 118) VHQVQLVQSGAEVKKPGASVKVSCKASGYTFTSYRMHWVRQAPGQGLEWMGFIVPSGGSTGYAQKFQGRVTMTRDTSTSTVYMELSSLRSEDTAVYYCARVSRYAPEPMDVWGQGTTVTVSS (SEQ ID NO: 119)CDR1: GYTFTSY (SEQ ID NO: 113; amino acid residues 26-32 of SEQ ID NO: 119)CDR2: VPSGGS (SEQ ID NO: 120; amino acid residues 52-57 of SEQ ID NO: 119)CDR3: VSRYAPEPMDV (SEQ ID NO: 121; amino acid residues 99-109 of SEQ ID NO: 119)H CAGGTGCAGCTGGTGCAGTCTGGGGCTGAGGTGAAGAAGCCTGGGGCCTCAGTGAAGGTTTCCTGCAAGGCATCTGGATACACCTTCACCTCGTACCGTATGCACTGGGTGCGACAGGCCCCTGGACAAGGGCTTGAGTGGATGGGATTTATCGTGCCTAGTGGTGGTAGCACAGGCTACGCACAGAAGTTCCAGGGCAGAGTTACCATGACCAGGGACACGTCCACGAGCACAGTCTACATGGAGCTGAGCAGCCTGAGATCTGAGGACACGGCGGTGTACTACTGCGCTAGAGTATCTAGGTACGCCCCAGAGCCAATGGACGTATGGGGCCAGGGAACAACTGTCACCGTCTCCTCAGCTAGCACAAAAGGACCAAGCGTGTTTCCACTGGCACCTAGCAGCAAATCCACCAGCGGCGGAACAGCAGCCCTCGGGTGCCTGGTGAAGGATTACTTCCCTGAGCCAGTCACAGTGTCCTGGAACTCCGGAGCCCTGACATCCGGCGTGCACACCTTCCCCGCTGTGCTGCAATCCAGCGGACTGTATAGCCTCAGCTCCGTCGTGACAGTCCCTTCCAGCAGCCTGGGCACACAGACTTACATTTGCAACGTGAACCACAAACCTTCCAACACTAAGGTGGACAAAAAGGTGGAACCCAAATCCTGTGATAAGACCCATACATGCCCACCTTGTCCCGCTCCTGAGCTGCTGGGGGGACCTTCCGTCTTTCTGTTTCCTCCAAAACCAAAAGACACACTCATGATCAGCCGGACCCCCGAAGTCACCTGTGTGGTGGTGGACGTCAGCCACGAAGATCCAGAGGTCAAGTTCAATTGGTACGTGGATGGAGTGGAAGTCCACAACGCAAAAACCAAACCTAGAGAAGAACAGTACAATAGCACATACAGGGTGGTGTCCGTCCTGACAGTGCTCCACCAGGACTGGCTCAATGGCAAAGAGTATAAGTGCAAGGTGAGCAACAAGGCCCTGCCTGCACCAATTGAGAAAACAATTAGCAAGGCAAAGGGGCAGCCACGGGAACCCCAGGTGTATACCCTGCCCCCAAGCCGGGATGAACTGACCAAAAACCAGGTCAGCCTGACATGCCTGGTGAAAGGGTTTTACCCAAGCGATATTGCCGTCGAGTGGGAGAGCAACGGACAGCCAGAAAACAATTACAAAACCACCCCACCTGTGCTGGACTCCGATGGGAGCTTTTTCCTGTACAGCAAGCTCACAGTGGACAAGTCCAGATGGCAACAGGGCAACGTGTTTTCCTGCTCCGTGATGCACGAGGCCCTCCACAACCACTATACACAAAAGTCCCTCTCCCTCAGCCCAGGAAAG (SEQ ID NO: 122) HQVQLVQSGAEVKKPGASVKVSCKASGYTFTSYRMHWVRQAPGQGLEWMGFIVPSGGSTGYAQKFQGRVTMTRDTSTSTVYMELSSLRSEDTAVYYCARVSRYAPEPMDVWGQGTTVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSVFLEPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFELYSKLTVDKSRWQQGNVESCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO: 123 VLDIQMTQSPSSVSASVGDRVTITCRASQGISRWLAWYQQKPGKAPKLLIYAASSLOSGVPSRFSGSGSGTDFTLTISSLQPEDFATYYCQQAFSHPWTFGGGTKVEIK (SEQ ID NO: 91)CDR1: RASQGISRWLA (SEQ ID NO: 92; amino acid residues 24-34 of SEQ ID NO: 91)CDR2: AASSLQS (SEQ ID NO: 153; amino acid residues 50-56 of SEQ ID NO: 91)CDR3: QQAFSHPWT (SEQ ID NO: 94; amino acid residues 89-97 of SEQ ID NO: 91)L SEQ ID NO: 95 L SEQ ID NO: 96 D04 VHCAGGTGCAGCTGGTGCAGTCTGGGGCTGAGGTGAAGAAGCCTGGGGCCTCAGTGAAGGTTTCCTGCAAGGCATCTGGATACACCTTCACCTCGTACCGTATGCACTGGGTGCGACAGGCCCCTGGACAAGGGCTTGAGTGGATGGGATTTATCGTGCCTAGTGGTGGTAGCACAGGCTACGCACAGAAGTTCCAGGGCAGAGTTACCATGACCAGGGACACGTCCACGAGCACAGTCTACATGGAGCTGAGCAGCCTGAGATCTGAGGACACGGCGGTGTACTACTGCGCTAGAGTATCTAGGTACGCCCCAGAGCCAATGGACGTATGGGGCCAGGGAACAACTGTCACCGTCTCCTCA (SEQ ID NO: 164) VHQVQLVQSGAEVKKPGASVKVSCKASGYTFTSYRMHWVRQAPGQGLEWMGFIVPSGGSTGYAQKFQGRVTMTRDTSTSTVYMELSSLRSEDTAVYYCARVSRYAPEPMDVWGQGTTVTVSS (SEQ ID NO: 165)CDR1: SYRMH (SEQ ID NO: 166; amino acid residues 31-35 of SEQ ID NO: 165)CDR2: FIVPSGGSTGYAQKFQG (SEQ ID NO: 167; amino acid residues 50-66 of SEQ ID NO: 165)CDR3: VSRYAPEPMDV (SEQ ID NO: 168; amino acid residues 99-109 of SEQ ID NO: 165) HCAGGTGCAGCTGGTGCAGTCTGGGGCTGAGGTGAAGAAGCCTGGGGCCTCAGTGAAGGTTTCCTGCAAGGCATCTGGATACACCTTCACCTCGTACCGTATGCACTGGGTGCGACAGGCCCCTGGACAAGGGCTTGAGTGGATGGGATTTATCGTGCCTAGTGGTGGTAGCACAGGCTACGCACAGAAGTTCCAGGGCAGAGTTACCATGACCAGGGACACGTCCACGAGCACAGTCTACATGGAGCTGAGCAGCCTGAGATCTGAGGACACGGCGGTGTACTACTGCGCTAGAGTATCTAGGTACGCCCCAGAGCCAATGGACGTATGGGGCCAGGGAACAACTGTCACCGTCTCCTCAGCTTCCACCAAGGGCCCATCCGTCTTCCCCCTGGCGCCCTGCTCCAGGAGCACCTCCGAGAGCACAGCCGCCCTGGGCTGCCTGGTCAAGGACTACTTCCCCGAACCGGTGACGGTGTCGTGGAACTCAGGCGCCCTGACCAGCGGCGTGCACACCTTCCCGGCTGTCCTACAGTCCTCAGGACTCTACTCCCTCAGCAGCGTGGTGACCGTGCCCTCCAGCAGCTTGGGCACGAAGACCTACACCTGCAACGTAGATCACAAGCCCAGCAACACCAAGGTGGACAAGAGAGTTGAGTCCAAATATGGTCCCCCATGCCCACCCTGCCCAGCACCTGAGTTCCTGGGGGGACCATCAGTCTTCCTGTTCCCCCCAAAACCCAAGGACACTCTCATGATCTCCCGGACCCCTGAGGTCACGTGCGTGGTGGTGGACGTGAGCCAGGAAGACCCCGAGGTCCAGTTCAACTGGTACGTGGATGGCGTGGAGGTGCATAATGCCAAGACAAAGCCGCGGGAGGAGCAGTTCAACAGCACGTACCGTGTGGTCAGCGTCCTCACCGTCCTGCACCAGGACTGGCTGAACGGCAAGGAGTACAAGTGCAAGGTCTCCAACAAAGGCCTCCCGTCCTCCATCGAGAAAACCATCTCCAAAGCCAAAGGGCAGCCCCGAGAGCCACAGGTGTACACCCTGCCCCCATCCCAGGAGGAGATGACCAAGAACCAGGTCAGCCTGACCTGCCTGGTCAAAGGCTTCTACCCCAGCGACATCGCCGTGGAGTGGGAGAGCAATGGGCAGCCGGAGAACAACTACAAGACCACGCCTCCCGTGCTGGACTCCGACGGCTCCTTCTTCCTCTACAGCAGGCTAACCGTGGACAAGAGCAGGTGGCAGGAGGGGAATGTCTTCTCATGCTCCGTGATGCATGAGGCTCTGCACAACCACTACACACAGAAGAGCCTCTCCCTGTCTCTGGGTAAATGA (SEQ ID NO: 169) HQVQLVQSGAEVKKPGASVKVSCKASGYTFTSYRMHWVRQAPGQGLEWMGFIVPSGGSTGYAQKFQGRVTMTRDTSTSTVYMELSSLRSEDTAVYYCARVSRYAPEPMDVWGQGTTVTVSSASTKGPSVFPLAPCSRSTSESTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSSSLGTKTYTCNVDHKPSNTKVDKRVESKYGPPCPPCPAPEFLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSQEDPEVQFNWYVDGVEVHNAKTKPREEQFNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKGLPSSIEKTISKAKGQPREPQVYTLPPSQEEMTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSRLTVDKSRWQEGNVFSCSVMHEALHNHYTQKSLSLSLGK (SEQ ID NO: 170) VLGACATCCAGATGACCCAGTCTCCATCTTCCGTGTCTGCATCTGTAGGAGACAGAGTCACCATCACTTGTCGGGCGAGTCAGGGTATTAGCAGGTGGTTAGCCTGGTATCAGCAGAAACCAGGGAAAGCCCCTAAGCTCCTGATCTATGCTGCATCCAGTTTGCAAAGTGGGGTCCCATCAAGGTTCAGCGGCAGTGGATCTGGGACAGATTTCACTCTCACCATCAGCAGCCTGCAGCCTGAAGATTTTGCAACTTATTACTGTCAGCAGGCATTCTCCCACCCTTGGACTTTTGGCGGAGGGACCAAGGTTGAGATCAAA (SEQ ID NO: 171) VLDIQMTQSPSSVSASVGDRVTITCRASQGISRWLAWYQQKPGKAPKLLIYAASSLQSGVPSRFSGSGSGTDFTLTISSLQPEDFATYYCQQAFSHPWTFGGGTKVEIK (SEQ ID NO: 172)CDR1: RASQGISRWLA (SEQ ID NO: 173; amino acid residues 24-34 of SEQ ID NO: 172)CDR2: AASSLQS (SEQ ID NO: 174; amino acid residues 50-56 of SEQ ID NO: 172)CDR3: QQAFSHPWT (SEQ ID NO: 175; amino acid residues 89-97 of SEQ ID NO: 172)L GACATCCAGATGACCCAGTCTCCATCTTCCGTGTCTGCATCTGTAGGAGACAGAGTCACCATCACTTGTCGGGCGAGTCAGGGTATTAGCAGGTGGTTAGCCTGGTATCAGCAGAAACCAGGGAAAGCCCCTAAGCTCCTGATCTATGCTGCATCCAGTTTGCAAAGTGGGGTCCCATCAAGGTTCAGCGGCAGTGGATCTGGGACAGATTTCACTCTCACCATCAGCAGCCTGCAGCCTGAAGATTTTGCAACTTATTACTGTCAGCAGGCATTCTCCCACCCTTGGACTTTTGGCGGAGGGACCAAGGTTGAGATCAAACGTAAGGGGCTCACAGTTAATTAATTGAGGTCTGGACATATACATGGGTGACAATGACATCCACTTTGCCTTTCTCTCCACAGGAACTGTGGCTGCACCATCTGTCTTCATCTTCCCGCCATCTGATGAGCAGTTGAAATCTGGAACTGCCTCTGTTGTGTGCCTGCTGAATAACTTCTATCCCAGAGAGGCCAAAGTACAGTGGAAGGTGGATAACGCCCTCCAATCGGGTAACTCCCAGGAGAGTGTCACAGAGCAGGACAGCAAGGACAGCACCTACAGCCTCAGCAGCACCCTGACGCTGAGCAAAGCAGACTACGAGAAACACAAAGTCTACGCCTGCGAAGTCACCCATCAGGGCCTGAGCTCGCCCGTCACAAAGAGCTTCAACAGGGGAGAGTGTTAG (SEQ ID NO: 176) LDIQMTQSPSSVSASVGDRVTITCRASQGISRWLAWYQQKPGKAPKLLIYAASSLQSGVPSRFSGSGSGTDFTLTISSLQPEDFATYYCQQAFSHPWTFGGGTKVEIKRTVAAPSVFIFPPSDEQLKSGTASVVCLLNNFYPREAKVQWKVDNALQSGNSQESVILQDSKDSTYSLSSTLTLSKADYEKHKVYACEVTHQGLSSPVTKSFNRGEC (SEQ ID NO: 177) ActRIIA-binding Antibodies G02 VHCAGGTGCAGCTGCAGGAGTCGGGCCCAGGACTGGTGAAGCCTTCACAGACCCTGTCCCTCACCTGTACTGTCTCTGGTGGCTCCATCAGCAGTGGTAGCTACTACTGGAGCTGGATCCGCCAGCACCCAGGGAAGGGCCTGGAGTGGATTGGGTACATCTATTACAGTGGGAGCACCTACTACAACCCGTCCCTCAAGAGTCGAGTTACCATATCAGTAGACACGTCTAAGAACCAGTTCTCCCTGAAGCTGAGTTCTGTGACCGCCGCAGACACGGCGGTGTACTACTGCGCCAGAGGACTAGGAATGTACTACCACGTGCCATTCGACATATGGGGTCAGGGTACAATGGTCACCGTCTCCTCA (SEQ ID NO: 124) VHQVQLQESGPGLVKPSQTLSLTCTVSGGSISSGSYYWSWIRQHPGKGLEWIGYIYYSGSTYYNPSLKSRVTISVDTSKNQFSLKLSSVTAADTAVYYCARGLGMYYHVPFDIWGQGTMVTVSS (SEQ ID NO: 125)CDR1: GGSISSGSY (SEQ ID NO: 126; amino acid residues 26-34 of SEQ ID NO: 125)CDR2: YYSGS (SEQ ID NO: 127; amino acid residues 54-58 of SEQ ID NO: 125)CDR3: GLGMYYHVPFDI (SEQ ID NO: 128; amino acid residues 100-111 of SEQ ID NO: 12) HCAGGTGCAGCTGCAGGAGTCGGGCCCAGGACTGGTGAAGCCTTCACAGACCCTGTCCCTCACCTGTACTGTCTCTGGTGGCTCCATCAGCAGTGGTAGCTACTACTGGAGCTGGATCCGCCAGCACCCAGGGAAGGGCCTGGAGTGGATTGGGTACATCTATTACAGTGGGAGCACCTACTACAACCCGTCCCTCAAGAGTCGAGTTACCATATCAGTAGACACGTCTAAGAACCAGTTCTCCCTGAAGCTGAGTTCTGTGACCGCCGCAGACACGGCGGTGTACTACTGCGCCAGAGGACTAGGAATGTACTACCACGTGCCATTCGACATATGGGGTCAGGGTACAATGGTCACCGTCTCCTCAGCTAGCACAAAAGGACCAAGCGTGTTTCCACTGGCACCTAGCAGCAAATCCACCAGCGGCGGAACAGCAGCCCTCGGGTGCCTGGTGAAGGATTACTTCCCTGAGCCAGTCACAGTGTCCTGGAACTCCGGAGCCCTGACATCCGGCGTGCACACCTTCCCCGCTGTGCTGCAATCCAGCGGACTGTATAGCCTCAGCTCCGTCGTGACAGTCCCTTCCAGCAGCCTGGGCACACAGACTTACATTTGCAACGTGAACCACAAACCTTCCAACACTAAGGTGGACAAAAAGGTGGAACCCAAATCCTGTGATAAGACCCATACATGCCCACCTTGTCCCGCTCCTGAGCTGCTGGGGGGACCTTCCGTCTTTCTGTTTCCTCCAAAACCAAAAGACACACTCATGATCAGCCGGACCCCCGAAGTCACCTGTGTGGTGGTGGACGTCAGCCACGAAGATCCAGAGGTCAAGTTCAATTGGTACGTGGATGGAGTGGAAGTCCACAACGCAAAAACCAAACCTAGAGAAGAACAGTACAATAGCACATACAGGGTGGTGTCCGTCCTGACAGTGCTCCACCAGGACTGGCTCAATGGCAAAGAGTATAAGTGCAAGGTGAGCAACAAGGCCCTGCCTGCACCAATTGAGAAAACAATTAGCAAGGCAAAGGGGCAGCCACGGGAACCCCAGGTGTATACCCTGCCCCCAAGCCGGGATGAACTGACCAAAAACCAGGTCAGCCTGACATGCCTGGTGAAAGGGTTTTACCCAAGCGATATTGCCGTCGAGTGGGAGAGCAACGGACAGCCAGAAAACAATTACAAAACCACCCCACCTGTGCTGGACTCCGATGGGAGCTTTTTCCTGTACAGCAAGCTCACAGTGGACAAGTCCAGATGGCAACAGGGCAACGTGTTTTCCTGCTCCGTGATGCACGAGGCCCTCCACAACCACTATACACAAAAGTCCCTCTCCCTCAGCCCAGGAAAG (SEQ ID NO: 129) HQVQLQESGPGLVKPSQTLSLTCTVSGGSISSGSYYWSWIRQHPGKGLEWIGYIYYSGSTYYNPSLKSRVTISVDTSKNQFSLKLSSVTAADTAVYYCARGLGMYYHVPFDIWGQGTMVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO: 130) VLGAAATTGTGTTGACACAGTCTCCAGCCACCCTGTCTTTGTCTCCAGGGGAAAGAGCCACCCTCTCCTGCAGGGCCAGTCAGAGTGTTAGCAGCTACTTAGCCTGGTACCAACAGAAACCTGGCCAGGCTCCCAGGCTCCTCATCTATGATGCATCCAACAGGGCCACTGGCATCCCAGCCAGGTTCAGTGGCAGTGGGTCTGGGACAGACTTCACTCTCACCATCAGCAGCCTAGAGCCTGAAGATTTTGCAGTTTATTACTGTCAGCAGTACTTCCACTGGCCTCCTACTTTTGGCGGAGGGACCAAGGTTGAGATCAAA(SEQ ID NO: 131) VLEIVLTQSPATLSLSPGERATLSCRASQSVSSYLAWYQQKPGQAPRLLIYDASNRATGIPARFSGSGSGTDFTLTISSLEPEDFAVYYCQQYFHWPPTFGGGTKVEIK (SEQ ID NO: 132)CDR1: RASQSVSSYLA (SEQ ID NO: 133; amino acid residues 24-34 of SEQ ID NO: 132)CDR2: DASNRAT (SEQ ID NO: 134; amino acid residues 50-56 of SEQ ID NO: 132)CDR3: QQYFHWPPT (SEQ ID NO: 135; amino acid residues 89-97 of SEQ ID NO: 132)L GAAATTGTGTTGACACAGTCTCCAGCCACCCTGTCTTTGTCTCCAGGGGAAAGAGCCACCCTCTCCTGCAGGGCCAGTCAGAGTGTTAGCAGCTACTTAGCCTGGTACCAACAGAAACCTGGCCAGGCTCCCAGGCTCCTCATCTATGATGCATCCAACAGGGCCACTGGCATCCCAGCCAGGTTCAGTGGCAGTGGGTCTGGGACAGACTTCACTCTCACCATCAGCAGCCTAGAGCCTGAAGATTTTGCAGTTTATTACTGTCAGCAGTACTTCCACTGGCCTCCTACTTTTGGCGGAGGGACCAAGGTTGAGATCAAACGTACGGTGGCTGCACCTTCCGTCTTTATCTTTCCACCTTCCGATGAGCAGCTGAAGAGCGGAACAGCAAGCGTGGTGTGTCTGCTGAACAACTTTTATCCCCGGGAGGCAAAGGTGCAGTGGAAAGTCGACAATGCTCTCCAGTCCGGCAATTCCCAAGAGAGCGTGACAGAGCAAGATTCCAAGGACTCCACTTACAGCCTGTCCAGCACCCTCACACTGAGCAAGGCTGATTACGAGAAACACAAAGTGTACGCTTGTGAAGTCACCCACCAAGGCCTGAGCAGCCCAGTCACTAAGTCCTTTAACCGGGGCGAATGT (SEQ ID NO: 136) LEIVLTQSPATLSLSPGERATLSCRASQSVSSYLAWYQQKPGQAPRLLIYDASNRATGIPARFSGSGSGTDFTLTISSLEPEDFAVYYCQQYFHWPPTFGGGTKVEIKRTVAAPSVFIFPPSDEQLKSGTASVVCLLNNFYPREAKVQWKVDNALQSGNSQESVFEQDSKDSTYSLSSTLTLSKADYEKHKVYACEVTHQGLSSPVTKSFNRGEC (SEQ ID NO: 137)

SPR (BIACORE™-based analysis) and cell-based reporter assay was used tomore fully characterize the binding of the ActRII-binding proteinsdescribed in Table 1.

A01 lineage Antibodies

Kinetic characterization of A01 antibody lineage (A01 (naïve parent),B01, C01, D01, E01 and F01) binding to monomeric and dimeric hActRIIBand hActRIIA was performed using standard BIACORE®-based analysis at 37°C. In brief, antibodies were captured on anti-hFcIgG Biacore chips anddifferent concentrations of dimeric and monomeric ActRIIB or ActRIIAwere injected in duplicates over the captured antibody and controlsurface. To obtain kinetic rate constants the data were doublereferenced and fit to a 1:1 interaction model using BiaEvaluationsoftware (GE Healthcare). The equilibrium binding constant K_(D) wasdetermined by the ratio of binding rate constants k_(d)/k_(a)

The results of the binding parameter analysis of the A01 lineageantibodies A01-F01 are presented in Table 2 and FIGS. 1A-1N.

TABLE 2 A01 lineage improved binding to ActRIIB ActRIIB MONOMER ActRIIBDIMER ActRIIA MONOMER ActRIIA DIMER k_(a) k_(d) K_(D) k_(a) k_(d) K_(D)k_(a) k_(d) K_(D) k_(a) k_(d) K_(D) mAb (1/Ms) (1/s) (pM) (1/Ms) (1/s)(pM) (1/Ms) (1/s) (pM) (1/Ms) (1/s) (pM) A01 1.72 × 10⁵ 1.98 × 10⁻⁻¹1150000 1.06 × 10⁵ 1.28 × 10⁻⁻⁴ 1207 No binding No binding Parent B011.09 × 10⁶ 3.40 × 10⁻⁻³ 3637 6.26 × 10⁵ 2.46 × 10⁻⁻⁴ 393 No binding Nobinding C01 1.37 × 10⁶ 7.12 × 10⁻⁻³ 5218 7.97 × 10⁵ 1.88 × 10⁻⁻⁴ 236 Nobinding No binding D01 1.61 × 10⁶ 3.54 × 10⁻⁻³ 2191 8.28 × 10⁵ 2.50 ×10⁻⁻⁴ 302 No binding No binding E01 1.70 × 10⁶ 4.15 × 10⁻⁻³ 2446 7.77 ×10⁵ 2.92 × 10⁻⁻⁴ 376 No binding No binding F01 1.34 × 10⁶ 4.44 × 10⁻⁻³3323 6.01 × 10⁵ 2.16 × 10⁻⁻⁴ 360 No binding No binding

The optimized A01 lineage antibodies B01, C01, D01, E01, and F01 eachdisplayed improved equilibrium dissociation constant (KD) kineticparameters for ActRIIB monomer and dimer binding over the A01 parentantibody.

The ActRIIB neutralizing ability of A01 lineage antibodies A01, B01,C01, D01, E01 and F01 was assessed in a cell-based activin A signalingassay in F2.35 (IIA knockout) cells obtained by CRISPE-Cas9 modificationof 293FT cells. Cells were co-transfected with experimental luciferasereporter plasmid containing Smad2/3 response element pGL3(CAGA)12 andcontrol luciferase reporter plasmid pRL-CMV. The next day, serialdilutions of the mAb was made and added to the transfected cells andincubated for 30 minutes, after which activating factors such as ActivinA was added (final concentration 5 ng/ml) for an additional 6 hourincubation. Cells were washed 1× in PBS, lysed and assayed using theDual-Luciferase Reporter Assay System (Promega) according to themanufacturer's instructions. Chemiluminescence was measured using theInfinite M200 plate reader. The luciferase activity of the experimentalreporter was normalized by the luciferase activity obtained from controlreporter. [. To evaluate anti-ActRIIA neutralizing activity, A204 cellswere transfected with the same reporter genes. A204 express ActRIIA anda low level of endogenous ActRIIB. The transfected cells were assayed asabove.

Each of the optimized A01 lineage antibodies, B01, C01, D01, E01, andF01, displayed increased ActRIIB-mediated signal inhibition compared tothe A01 parent antibody. See, FIG. 2.

G01 Lineage Antibodies

Kinetic characterization of the G01 (naïve parent) and optimized H01antibodies to monomeric and dimeric hActRIIB and hActRIIA was performedusing standard BIACORE®-based analysis at 37° C.

The results of the binding parameter analysis of the G01 and H01antibodies are presented in Table 3 and FIGS. 3A-3F.

TABLE 3 G02 lineage improved binding to ActRIIB ActRIIB MONOMER ActRIIBDIMER ActRIIA MONOMER ActRIIA DIMER k_(a) k_(d) K_(D) k_(a) k_(d) K_(D)k_(a) k_(d) K_(D) k_(a) k_(d) K_(D) mAb (1/Ms) (1/s) (pM) (1/Ms) (1/s)(pM) (1/Ms) (1/s) (pM) (1/Ms) (1/s) (pM) G01 9.05 × 10⁵ 1.52 × 10⁻⁻²16790 1.76 × 10⁵ 2.20 × 10⁻⁻⁴ 1139 No binding No binding Parent H01 1.95× 10⁶ 2.30 × 10⁻⁻² 11790 3.58 × 10⁵ 1.27 × 10⁻⁻⁴ 353 No binding Nobinding

The H02 optimized antibody displayed improved equilibrium dissociationconstant (KD) kinetic parameters for ActRIIB monomer and dimer bindingover the G01 parent antibody.

The ActRIIB neutralizing ability of the parent G01 and optimized H01antibodies was assessed in a cell-based activin A signaling assay inF2.35 (IIA knockout) cells. The H01 optimized antibody displayed anincreased ActRIIB-mediated signal inhibition compared to the G01 parentantibody. See, FIG. 4.

A02 Lineage Antibodies

Kinetic characterization of A02 antibody lineage (A01 (naïve parent),B02, C02, D02, and D03) binding to monomeric and dimeric hActRIIB andhActRIIA was performed using standard BIACORE®-based analysis at 37° C.

The results of the binding parameter analysis of the A02 lineageantibodies A02-D02 are presented in Table 4 and FIGS. 5A-5T.

TABLE 4 A02 lineage improved binding to ActRIIB and ActRIIA ActRIIBMONOMER ActRIIB DIMER ActRIIA MONOMER ActRIIA DIMER k_(a) k_(d) K_(D)k_(a) k_(d) K_(D) k_(a) k_(d) K_(D) k_(a) k_(d) K_(D) mAb (1/Ms) (1/s)(pM) (1/Ms) (1/s) (pM) (1/Ms) (1/s) (pM) (1/Ms) (1/s) (pM) A02 3.02 ×10⁶ 6.62 × 10⁻² 21960 2.19 × 10⁵ 1.12 × 10⁻⁴ 511 No binding 3.53 × 10⁵6.27 × 10⁻⁴ 1777 Parent B02 9.05 × 10⁵ 1.00 × 10⁻³ 1105 3.23 × 10⁵ 2.10× 10⁻⁴ 649 7.29 × 10⁶ 5.93 × 10⁻³ 8134 4.95 × 10⁵ 1.67 × 10⁻⁴ 338 C029.75 × 10⁵ 5.15 × 10⁻⁴ 528 2.89 × 10⁵ 9.64 × 10⁻⁵ 333 6.30 × 10⁶ 1.66 ×10⁻³ 26370 5.24 × 10⁵ 8.02 × 10⁻⁵ 153 D02 4.47 × 10⁵ 2.91 × 10⁻⁴ 6501.70 × 10⁵ 1.23 × 10⁻⁴ 727 3.69 × 10⁶ 6.84 × 10⁻³ 18560 3.36 × 10⁵ 1.06× 10⁻⁴ 316 D03 1.05 × 10⁶ 2.03 × 10⁻⁴ 194 4.59 × 10⁵ 1.04 × 10⁻⁵ 22.68.09 × 10⁵ 2.93 × 10⁻³ 3635 4.71 × 10⁵ 9.39 × 10⁻⁵ 199

The optimized A02 lineage antibodies B02, C02, D02, and D03 eachdisplayed improved equilibrium dissociation constants (KD) for bindingActRIIB and ActRIIA monomers, and ActRIIA dimers over the A02 parentantibody.

The ActRIIB neutralizing ability of antibodies A02, B02, C02, D02, andD03 was assessed in a cell-based activin A signaling assay in F2.35 (IIAknockout) cells. Each of the optimized antibodies, B02, C02, D02, andD03 displayed increased ActRIIB-mediated signal inhibition compared tothe A02 antibody. See, FIGS. 6A-6B.

E02 Lineage Antibodies

Kinetic characterization of the E02 (naïve parent) and optimized F02antibodies to monomeric and dimeric hActRIIB and hActRIIA was performedusing standard BIACORE®-based analysis at 37° C.

The results of the binding parameter analysis of the E02 and F02antibodies are presented in Table 5 and FIGS. 7A-7F.

TABLE 5 E02 lineage improved binding to ActRIIB ActRIIB MONOMER ActRIIBDIMER ActRIIA MONOMER ActRIIA DIMER k_(a) k_(d) K_(D) k_(a) k_(d) K_(D)k_(a) k_(d) K_(D) k_(a) k_(d) K_(D) mAb (1/Ms) (1/s) (pM) (1/Ms) (1/s)(pM) (1/Ms) (1/s) (pM) (1/Ms) (1/s) (pM) E02 1.02 × 10⁵ 6.92 × 10⁻⁴ 67983.81 × 10⁴ 7.60 × 10⁻⁵ 1995 No binding No binding F02 1.19 × 10⁵ 3.13 ×10⁻⁴ 2632 4.69 × 10⁴ 3.46 × 10⁻⁵ 738 No binding No binding

The F02 optimized antibody displayed improved kinetic parametersequilibrium dissociation constant (KD) over for ActRIIB monomer anddimer binding over over the E02 parent antibody.

The ActRIIB neutralizing ability of the E02 and F02 antibodies wasassessed in a cell-based activin A signaling assay in F2.35 (IIAknockout) cells. FIG. 9 depicts the neutralizing activity of E02 parentand F02 variant antibodies in the assay. As demonstrated, the F02antibody displayed increased signal inhibition compared to the E02.

G02 Antibody

Kinetic characterization of G02 antibody binding to monomeric anddimeric hActRIIB and hActRIIA was performed using standardBIACORE®-based analysis at 37° C. FIGS. 8A-8D show kineticcharacterization of G02 antibody binding to monomeric and dimerichActRIIB and hActRIIA (FIG. 8A-8D, respectively) as determined byBIACORE®-based analysis at 37° C. The results of the binding parameteranalysis of the G02 antibody is presented in Table 6.

TABLE 6 G02 antibody binding to ActRIIA ActRIIB MONOMER ActRIIB DIMERActRIIA MONOMER ActRIIA DIMER k_(a) k_(d) K_(D) k_(a) k_(d) K_(D) k_(a)k_(d) K_(D) k_(a) k_(d) K_(D) mAb (1/Ms) (1/s) (pM) (1/Ms) (1/s) (pM)(1/Ms) (1/s) (pM) (1/Ms) (1/s) (pM) G02 No binding No binding 1.14 × 10⁶6.61 ×10⁻² 58020 1.86 × 10⁵ 2.75 × 10⁻⁴ 1480

Example 3. Reporter Gene Assay in A204 Cells

A reporter gene assay in A204 cells can be used to determine the abilityof ActRII-binding proteins such as anti-ActRII Fabs and recombinantantibodies to neutralize ActRII (e.g., ActRIIB). This assay can be basedon a human rhabdomyosarcoma cell line transfected with a pGL3(CAGA)12reporter plasmid (Dennler et al., EMBO 17:3091-3100 (1998)) as well as aReniUa reporter plasmid (pRLCMV) to control for transfection efficiency.The CAGA12 motif is present in TGF-beta responsive genes (PAI-1 gene),so this vector is of general use for factors signaling through Smad2 andSmad3. Since the A204 cell line expresses primarily ActRIIA rather thanActRIIB, it is not possible to directly test antibodies for potentialActRIIB neutralizing ability. Instead, this assay can be designed todetect the ability of test articles to neutralize the inhibitory effectof the soluble fusion protein ActRIIB-Fc on activation of endogenousActRIIA by ligands (such as activin A, GDF11, or myostatin) that canbind with high affinity to both ActRIIB and ActRIIA.

Thus, in this assay, ligand-mediated activation of ActRIIA will occurdespite the presence of ActRIIB-Fc if the anti-ActRIIB Fab or antibodyis neutralizing. On the first day of the assay, A204 cells (ATCC HTB-82)are distributed in 48-well plates at 10⁵ cells per well. On the secondday, a solution containing 10 μg pGL3(CAGA)12, 1 μg pRLCMV, 30 μl Fugene6 (Roche Diagnostics), and 970 μl OptiMEM (Invitrogen) is preincubatedfor 30 min, then added to McCoy's growth medium, which is applied to theplated cells (500 μl/well) for incubation overnight at room temperature.On the third day, medium is removed, and cells are incubated for 6 h at37° C. with a mixture of ligands and inhibitors prepared as describedbelow.

To evaluate the neutralizing potency of test ActRII-binding proteins, aserial dilution of the test article is made in a 48-well plate in a 200μl volume of assay buffer (McCoy's medium +0.1% BSA). An equal volume ofActRIIB-Fc (200 μg/ml) in assay buffer is then added. The test solutionsare incubated at 37° C. for 30 minutes, then 400 μl of GDF11 (10 ng/ml)or activin A (10 ng/ml) is added to all wells, and 350 ii of thismixture is added to each well of the 48-well plate of A204 cells. Eachconcentration of test ActRII-binding protein is tested in duplicate. Thefinal concentration of ActRIIB-Fc is 50 ng/ml (which is the IC₅₀ forthis inhibitor of activin A signaling when the final concentration ofactivin A is 5 ng/ml). After incubation with test solutions for 6 h,cells are rinsed with phosphate-buffered saline containing 0.1% BSA,then lysed with passive lysis buffer (Promega El 941) and storedovernight at −70° C. On the fourth and final day, plates are warmed toroom temperature with gentle shaking. Cell lysates are transferred induplicate to a chemoluminescence plate (96-well) and analyzed in aluminometer with reagents from a Dual-Luciferase Reporter Assay system(Promega El 980) to determine normalized luciferase activity.Differences in luciferase activity between the test article and acontrol in which the test article is absent reflect differences incellular signaling resulting from the presence of the test article.

Example 4. Precision Epitope Mapping

Mapping of the ActRIIB and ActRIIA ECD epitopes recognized by theantibodies was performed by Pepscan Presto BV using custom made peptidelibraries. Sequences of ECDs of human ActRIIB and ActRIIA were convertedinto libraries of overlapping linear 15-mers and circularized 15-merCLIPS using combinatorial matrix design. CLIPS (Chemical Linkage ofPeptides onto Scaffolds) technology structurally fixes peptides intodefined three-dimensional structures (single, double, triple, etc.loops) creating functional mimics of complex binding sites. Peptideswere synthesized on solid support. Binding of antibodies to each of thesynthesized peptides was tested by ELISA and binding affinities werequantified. Peptide constructs representing both parts of thediscontinuous epitope in the correct conformation bind specific antibodywith the highest affinity. Peptide constructs presenting an incompleteepitope bind specific antibody with lower affinity, whereas constructsnot containing correct epitope did not bind at all. Each peptide wasgiven a score based on affinity.

Antibody D04 was determined to bind across three sequence stretches onAcRIIA, with binding epitopes mapped to amino acid residues 9 through to20 (ECLFFNANWEKD (SEQ ID NO:162)), amino acid residues 58 through to 69(CWLDDINCYDRT (SEQ ID NO:163)) and amino acid residues 84 through to 93(CCEGNMCNEK (SEQ ID NO:161)) of SEQ ID NO: 138.

Antibody D04 was also determined to bind across three sequence stretcheson AcRIIB, with binding epitopes mapped to amino acids 9 through to 17(NANWELERT (SEQ ID NO:157)), amino acids 52 through to 63 (GCWLDDFNCYDR(SEQ ID NO:160)) and a binding site of amino acids 79 through to 88(CCEGNFCNER (SEQ ID NO:159)) of SEQ ID NO: 138.

Antibody 101 was determined to bind across two stretches of sites onAcRIIB, with binding epitopes mapped to amino acids 9 through to 17(NANWELERT (SEQ ID NO:157)) and amino acids 49 through to 63 (VKKGCWLDD(SEQ ID NO:158)) of SEQ ID NO: 139.

The invention claimed is:
 1. A method for increasing muscle mass in asubject, comprising administering to a subject in need thereof anActRII-binding antibody comprising a set of CDRs in which: (i) VH-CDR1has the amino acid sequence of SEQ ID NO:166; (ii) VH-CDR2 has the aminoacid sequence of SEQ ID NO:167; (iii) VH-CDR3 has the amino acidsequence of SEQ ID NO:168; (iv) VL-CDR1 has the amino acid sequence ofSEQ ID NO:173; (v) VL-CDR2 has the amino acid sequence of SEQ ID NO:174;and (vi) VL-CDR3 has the amino acid sequence of SEQ ID NO:175; andwherein the antibody binds ActRIIB.
 2. The method of claim 1, whereinthe subject has a disease or condition selected from a degenerativemuscle disease, muscular dystrophy, muscle atrophy, and muscle wasting.3. The method of claim 1, wherein the ActRII-binding antibody isadministered alone or as part of a combination therapy.
 4. The method ofclaim 1, wherein the ActRII-binding antibody comprises a VH sequence ofSEQ ID NO:165 and a VL sequence of SEQ ID NO:172.
 5. The method of claim1, wherein the ActRII-binding antibody has at least one characteristicselected from: (a) competing with activin A, activin B, BMP7, BMP9,BMP10, GDF8 (myostatin), GDF11, or Nodal, for binding to ActRIIB orActRIIA; (b) decreasing the phosphorylation of one or more Smads incells expressing ActRIIB and/or ActRIIA in the presence of an ActRIIB orActRIIA ligand; (c) decreasing the phosphorylation of ALK4 or ALK7 incells expressing ActRIIB or ActRIIA and ALK4 or ALK7 in the presence ofan ActRIIB or ActRIIA ligand; and (d) binding to ActRIIB or ActRIIA witha KD of ≤1 nM and ≥1 pM, as determined by BIACORE® analysis.
 6. Themethod of claim 1, wherein the ActRII-binding antibody is a monoclonalantibody, a recombinant antibody, a human antibody, a humanizedantibody, a chimeric antibody, a bi-specific antibody, a multi-specificantibody, or an ActRII-binding antibody fragment.
 7. The method of claim6, wherein the ActRII-binding antibody fragment is a Fab fragment, aFab′ fragment, a F(ab′)2 fragment, an Fv fragment, a diabody, or asingle chain antibody molecule.
 8. The method of claim 6, wherein theActRII-binding antibody further comprises a heavy chain immunoglobulinconstant domain selected from: (a) a human IgA constant domain; (b) ahuman IgD constant domain; (c) a human IgE constant domain; (d) a humanIgG1 constant domain; (e) a human IgG2 constant domain; (f) a human IgG3constant domain; (g) a human IgG4 constant domain; and (h) a human IgMconstant domain.
 9. The method of claim 6, wherein the ActRII-bindingantibody further comprises a light chain immunoglobulin constant domainselected from: (a) a human Ig kappa constant domain; and (b) a human Iglambda constant domain.
 10. The method of claim 6, wherein theActRII-binding antibody further comprises a human IgG1 heavy chainconstant domain and a human lambda light chain constant domain.